Question 4284
D = R*T

Let S = Rate in still air
 S + 60 = Rate eastbound
 S - 60 = Rate westbound
    4 hours = Time eastbound
    5 hours = Time westbound


Distance traveled eastbound = Distance traveled westbound.
4(S + 60) = 5 (S - 60)
4S + 240 = 5S - 300


Add -4S to each side to get all variables to the right side
4S - 4S + 240 = 5S - 4S - 300
          240 =  S - 300


Add 300 to each side:
          240 + 300 = S - 300 + 300
                540 MPH = S