Question 1058586
Let x represent his speed on the "good road".


If he travels 29 km at this speed, the time taken is 29/x hours.


His speed on the "bad road" would be x - 42.


If he travels 15 km at this speed, the time taken is 15/(x - 42) hours.


Since it takes him the same time to cover both distances, you can write:


29/x = 15/(x - 42)


Multiplying both sides by x gives:


29 = 15x/(x - 42)


Then multiplying both sides by (x - 42) leaves:


29(x - 42) = 15x


29x - 1218 = 15x


29x - 15x = 1218


14x = 1218


x = 87 km/hr


Solution: His speed on the good road is 87 km/hr. His speed 
on the bad road would be 87 - 42 = 45 km/hr.