Answer:
Luis and David live 23 miles apart.
Explanation:
They ride in opposite direction(west, east), so we add the distances that both traveled, and this is how far apart they live.
Luis
Luis rides at an average speed of 24 miles per hour. He rides for 20 minutes, which is 1/3 of an hour. 24/3 = 8. This means that Luis rode for 8 miles.
David
David rides at an average speed of 20 miles per hour. He rides for 45 minutes, which is 3/4 of an hour. So 3*20/4 = 15 miles. David rides for 15 miles.
8+15 = 23.
So Luis and David live 23 miles apart.