Let the speed of the freight train be x mph.
Then the speed of the passenger train is (x + 11) mph.
Distance traveled by the freight train in 20 hours = 20x miles.
The passenger train has 20 - 4 = 16 hours to pass the freight train after traveling 20x miles at (x + 11) mph.
\(Speed=\frac{distance}{time}\)
\(x+11=\frac{20x}{16}\)
16x + 176 = 20x
4x = 176
x = 44
The speed of the freight train is 44 mph and the speed of the passenger train is 55 mph.