This is a PERT (Program Evaluation and Review Technique) estimation problem. The formula used is:
Expected Duration (TE) = (Optimistic + 4×Most Likely + Pessimistic) / 6
= (5 + 4×11 + 20) / 6
= (5 + 44 + 20) / 6
= 69 / 6 = 11.5 # Rounded = 12 days
While 11.5 is the exact mathematical output, PMI-style questions typically round this to the nearest whole number when appropriate.
Thus, the correct answer is C. 12 days
References:
PMBOK Guide - Seventh Edition, Planning Performance Domain
PMI Practice Standard for Scheduling

A hybrid project management methodology is a combination of two or more different approaches to delivering projects, such as waterfall and agile1. Hybrid projects can offer benefits such as flexibility, adaptability, customer satisfaction, and innovation2. However, hybrid projects also require frequent reviews and feedback loops to ensure alignment, collaboration, and quality among the project team and stakeholders3. Therefore, the project manager should explain to the stakeholder the value of attending the iteration reviews, which are opportunities to inspect the project deliverables, provide feedback, identify issues, and plan for the next iteration4. By doing so, the project manager can demonstrate how the stakeholder's involvement can contribute to the project success and avoid potential rework or waste. References:
* Ultimate Guide To Hybrid Project Methodologies & How To Make Them
* Hybrid project management - the key to a successful future? - APM
* Hybrid project management - a systematic literature review ...
* TOWARDS A HYBRID PROJECT MANAGEMENT FRAMEWORK: A SYSTEMATIC
LITERATURE ...

Earned Value Analysis (EVA) is a project management technique used for monitoring and controlling project performance by integrating scope, schedule, and cost parameters. It is a critical tool for project managers to report the project's value and is particularly useful for large projects where tracking progress against the budget is essential. EVA provides a set of mathematical metrics that reflect the health of the project and is used to report information for the current reporting period and on a cumulative basis. This method allows project managers to identify variances from the plan and forecast future performance, which is crucial for seeking further funding and demonstrating the project's value to sponsors.
: (Earned Value Analysis & Management (EVA/EVM) - Project-Management.info1, Professional in Business Analysis Reference Materials | PMI2)

The project manager should work with the client on an acceptable amount of time for document approval, as this is the best way to address the issue of slow turn-around times and avoid potential delays in the new project. By collaborating with the client, the project manager can establish a mutual understanding of the expectations, requirements, and constraints of the document approval process, and negotiate a realistic and feasible timeline that satisfies both parties. This will also help the project manager to build trust and rapport with the client, and foster a positive and cooperative relationship.