Let x denote the number of kilometers of the road in good condition. Then (48 - x) is the number of kilometers of the road in bad condition.

From the definition of you get

Now you can set up an equation in x:

(Keep in mind that the speed is given in kilometers perhourand the elapsed time in minutes, which have to be changed to hours too!)

Solve the equation above for x. I've got x = 36 km. Consequently the bad road is 12 km long.