Help solve this for me

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?

-define the x's

Answer 1

Distance = rate × time or d = rt

Let x = the outbound rate and x-7 = the inbound rate. The distance to and from are the same.

12x = 15(x-7)

12x = 15x-105

3x= 105

x = 35 km/h

Answer 2

d_there = 12(r + 7)

d_back = 15r

d_there = d_back

Can you solve for r and answer?