The best way to calculate an overdue date that is two months after a task due date is to use a formula field with the ADDMONTHS() function. This function adds a specified number of months to a date value, and returns a new date value. See [this article] for more information on formula fields.

The best way to solve this problem is to filter components by device using Form Factor. Form Factor is an attribute that can be applied to components on a Lightning record page to control their visibility based on the device type, such as desktop, phone, or tablet. By using Form Factor, the app builder can hide some components that are not relevant for mobile users, such as charts or reports, and show only the components that are necessary for data entry, such as fields or actions. This way, the mobile users do not have to scroll through all the components and can enter data more easily. Reordering the fields may not solve the problem completely, as there may still be too many components on the page for mobile users. Updating the training documentation may not help either, as it does not address the root cause of the problem, which is the layout of the page. Deselecting the phone radio button on the Lightning record page assignment may not be desirable, as it will prevent mobile users from accessing the record page at all, which may affect their productivity and functionality.

The formula for creating a visual indicator flag on each case based on the case priority should use the IMAGE and CASE functions. The IMAGE function returns an image for a given URL, and the CASE function evaluates an expression and returns a value based on that expression. Option A and D use these functions correctly, while option B and C do not.

The app builder needs to do two steps to make the custom Lightning App available to the internal users at Universal Containers:
Create a subdomain using My Domain: My Domain is a feature that allows an organization to set up a custom domain name for their Salesforce instance. This is required to use custom Lightning components and apps in Salesforce1.
Build a Custom Tab for the app: A custom tab is a tab that displays any custom object or web page in Salesforce. This is required to make the custom Lightning App accessible from the navigation menu or app launcher2. Option A and B are not necessary steps to make the custom Lightning App available to the internal users.

Standard buttons can be overridden with a Visualforce page to provide custom functionality or user interface. For example, you can override the New button on an object to display a custom Visualforce page instead of the standard page layout3. Standard buttons that are not available for overrides can still be hidden on page layouts to prevent users from accessing them. For example, you can hide the Delete button on an object to prevent users from deleting records