A company is in the final phases of implementing a project for a client. Which tool or technique could the business analyst use to iteratively validate the solution?

Company A is working on implementing a new platform with multiple stakeholders. The business analyst has gathered the requirements and established a baseline. However, scope creep is a persistent problem.
What could the business analyst have established to help manage this situation?

A national company with offices in every stale in the country has deployed a solution to allow employees to view their health benefits online. The business analyst on the project team is validating solution results to assess whether or not the solution has achieved the desired business result.
Which is the best technique to gather information from employees regarding their satisfaction with the solution?

A new project's goal is to replace an existing system. What is an input into solution evaluation and decision making in this context?

Once the requirements are compared to internal and external quality standards, what should the business analyst do next?