let

v = the speed of the slower train, v>0

v + 25 = the speed of the faster train

d = 200 mi the distance traveled

t + 4 = the time of the slower train

t = the time of the faster train

since speed = distance/time follows distance = speed*time

for the slower train we have:

v(t + 4) = d

v(t + 4) = 200

for the faster train we have:

(v + 25)*t = d

(v + 25)*t = 200

t = 200/(v + 25)

plug t = 200/(v + 25) into v(t + 4) = 200

v(200/(v + 25) + 4) = 200

by solving we find:

v = 25 mph

click here to see the step by step solution of the equation:

v + 25 = 25 + 25 = 50 mph

the speed of the slower train is 25 mph.

the speed of the faster train is 50 mph.