In payroll, deductions are applied in a priority order so employers satisfy mandatory legal obligations first.
CRA collection tools such as a Requirement to Pay (RTP) and a Demand on a Third Party (DTP) are legal
/garnishment-type deductions. CRA explains that a Requirement to Pay directs a third party (often the employer) to send amounts otherwise payable to the employee to the CRA, and the employer must comply.
Company pension contributions (where participation is required as a condition of employment or under a plan
/collective agreement) are generally company-compulsory deductions-important, but they come after statutory and legal deductions. Voluntary insurance coverage is a classic voluntary deduction (the employee chooses it; it is not legally required). Voluntary deductions are normally taken last because they must not interfere with statutory/legal withholding obligations.
So among the options, voluntary insurance coverage is the one that would be withheld last in the order of priority.

The CRA form used to adjust payroll income tax withholdings at source for employees who earn commission income and have commission expenses is Form TD1X - Statement of Commission Income and Expenses for Payroll Tax Deductions. The CRA explains that an employee completes TD1X if they receive commission income (or salary plus commission) and want the employer to adjust tax deductions to take commission expenses into account.
This is different from:
TD1, which is the Personal Tax Credits Return used to claim basic/personal credits and determine standard withholding (not commission-expense adjustments).
T777, which is used to claim employment expenses on the employee's personal tax return (not to reduce payroll withholding at source).
TP-1015.R.13.1-V, which is a Quebec form used to request a reduction of Quebec income tax withholding in specific situations (not the CRA commission-expense at-source form).
Operationally, payroll should keep the TD1X on file and apply it to income tax withholding calculations until the employee updates or replaces it.

Block 11 on the ROE is the "Last day for which paid," meaning the last day the employee received insurable earnings. In most terminations, this is the employee's last day of work. Service Canada notes Block 11 only moves beyond the last day worked when the employee continues to receive insurable earnings after the last day of work due to paid leave (such as vacation leave or sick leave) or salary continuance.
In this question, Charmaine's employment ended April 13, and she received a lump-sum final pay that included wages in lieu of notice and vacation pay. These amounts are typically reported as special payments (for example, pay in lieu of notice is reported as such), but they do not automatically change Block 11 unless they are paid as an actual paid-leave period or as salary continuance (where regular pay continues and the ROE is not issued until the continuance ends).

$712.00
Explanation:
For payroll income tax purposes, net taxable income starts with the employee's gross taxable income and then subtracts only those deductions that are deductible for income tax and can be recognized at source. CRA payroll guidance shows this approach by subtracting items such as RPP contributions and union dues when determining net taxable income for calculating income tax deductions.
Gross taxable income (weekly): $750.00.
RPP contributions are deductible (the amounts reported from box 20 of the T4 are generally deductible).
Regular union dues are deductible; however, the CRA states that deductible annual union/professional dues do not include special assessments or charges for anything other than ordinary operating costs. A levy specifically for constructing a new union hall is a special assessment, so it is not deductible as union dues.
So the deductions that reduce federal taxable income here are: $18.00 (union dues) + $20.00 (RPP) = $38.00.
Net federal taxable income = $750.00 # $38.00 = $712.00.

Overtime premiums and piece-rate pay are forms of earnings because they are amounts paid for work performed. CRA's payroll guidance confirms overtime pay is remuneration from which you must deduct statutory deductions (CPP, EI, and income tax), reflecting that overtime is treated as employment earnings.
Similarly, piecework (piece-rate pay) is a method of paying wages based on units produced rather than time.
It is still compensation for labour and therefore part of gross earnings used to calculate payroll deductions and net pay. This is fundamentally different from:
Expense reimbursements, which repay employee-incurred business costs (not pay for work).
Allowances, which are predetermined amounts to help cover anticipated expenses without receipts.
Benefits, which are the value of goods/services provided by the employer or paid on the employee's behalf.
So a premium paid for overtime hours or a piece-rate per unit produced is classified as earnings (option A).