A car moved from a position 50 miles south of the library to a new position 250 miles north of the library. This movement takes 15 seconds. What is the velocity of the car

Velocity is the speed and direction.

It started 50 miles south, then ended up 250 miles north, so it's heading north.

The total distance is 300 miles, cause you just combine them.

Then speed is distance/time so

300 miles / 15 seconds is 20 miles/second