Help me solve this problem

Question

A diesel train made a trip to the outer-most station and back. The trip there took 12 hours and the trip back took 15 hours. It averaged 7 km/h faster on the trip there than on the return trip. What was the diesel train average speed on the outbound trip?

Answer 1

rate * time = distance

let x be rate for inbound:

distance outbound = outbound rate * time outbound = (x+ 7) * 12

distance inbound = inbound rate * time inbound = x * 15

distance the same

(x + 7) * 12 = 15 x

12x + 84 = 15x

3x = 84

x = 28

average speed on outbound is 28