The general formula is
D(istance) = R(ate of speed) x T(ime in portions of an hour)
So the question gives you the distance and rate of speed, so what should you do?
Info you're given:
D = 80 miles
R = 50 mph
T = how long does it take
So you need to figure out how to adapt the general formula. I'll bet you can do that part and come up with answer yourself.