Acar drives 215 km east and then 45 km north. what is the magnitude of the car’s displacement? round your answer to the nearest whole number.

You use the Theorem of Pythagoras:
Imagine the Car is driving: when it turns left to drive north This has to be an 90 degree angle:
^
---> |

But the displacement is Always the shortest Line between the start and the end and in This case it is a Line which creates a triangle.
In a triangle With a right angle you can use Pythagoras:
215^2+45^2=c^2
v=√(215^2+45^2)