Question 236977
Formula is d=r*t
Train A   d=100(t+1)
Train B   d=125t
Substitue 125t for d
125t=100(t+1)
Multiply to remove parentheses on the right
125t=100t+100
25t=100
Divide 100 by 25 = 4
Answer is 4 hours later or 1:20am

To check the answer:
Find the distance that is traveled
Train B   125*4=500 miles
Train A   4+1*100=500 miles

Both trains travel the same distance