Answer:
since the rate is the same for both trains, and we know that the distance train A travels plus the distance train B travels equals 562.5 miles, we can use the D(istance) = R(ate) * T(ime) formula to solve this.
Train A:
da = R * 4
Train B:
db = R * 3.5 (using 3.5 instead of 3 and 1/2)
Solve for R:
R * 4 + R * 3.5 = 562.5
7.5 * R = 562.5
R = 75
The trains are traveling at 75 miles per hour.
Explanation: