Solve the each part of given question:
Question: A man in search of his dog drives first 12.5 mi northeast, then 16.5 mi straight south, and finally 6.31 mi in a direction 32.1° north of west.
Part A: What is the magnitude of his resultant displacement?
Part B: What is the direction of his resultant displacement? Express your answer counterclockwise relative to the positive x-axis.
I know the correct answer but explain how to get this answer!