It took Nina one hour longer to drive to her brother's house than it did to return home. If it took Nina 6 hours to make the round trip and she traveled 20 mph faster on the return trip, how fast did she drive on the way to her brother's house?
time = distance/speed. So if the distance is d, we have
d/(s-20) = d/s + 1
d/(s-20) + d/s = 6
So, d=175 miles and the trip to was driven at 50 mi/hr
175/50 = 3.5 hours to go
and
175/70 = 2.5 hours to return