Jim and mark start at the same place jim walks 15ft west and mark walks 12 feet north how far apart are the boys when they finish walking

The two points where they end and the point where they start form a right triangle, one leg is 12, the other leg is 15, you need to find the hypotenuse.
use the Pythagorean theorem: 12²+15²=c²
c≈19
they are about 19 feet apart.