Harry and selma start driving from the same location. harry drives 42 miles north while selma drives 144 miles east. how far apart are harry and selma when they stop?

North and East are perpendicular, so you are actually asked to find the hypotenuse of a right triangle with one leg 42 miles long the other 144 miles long.
use the Pythagorean theorem, 42^2+144^2=22500, √22500=150
so they are 150 miles apart.