Explanation
The purpose of requirements traceability is to trace where each requirement or design comes from or originated from and what its life cycle is throughout the project. If it is known why a requirement exists, or where it originated from, it will ensure that once the solution has been delivered, it does in actual fact solve the original requirement. By knowing where a requirement came from, or what the need that should be addressed is, the business analyst will know who to communicate to as well as be able to manage the risk, scope, and any changes associated with that requirement.

Explanation
In 105 months, your solution will equate to the cost savings offered by the vendor. In other words, if your solution will be kept longer than
105 months, it's best to use your solution. You can find this solution by first finding the difference of the build and buy costs, which is $47,000. Next, find the difference of the monthly costs, which is only $450. You'll then divide $47,000 by $450 for an answer of 104.4 months, or for this answer, 105 months.
Answer C is incorrect. 64 months is not the correct calculation to this scenario. Answer B is incorrect. 32 months is not the correct calculation to this scenario. Answer D is incorrect. 19 months is not the correct calculation to this scenario.

Reference:
BABOK v.3.0 - IIBA - A Guide to the Business Analysis Body of Knowledge - International Institute of Business Analysis (2015) (Page 37)