A man drives from city to village a distance of 48 km ,in 45 minutes. Where the road surface is good , he drives at 72 km/hr and where it is bad , at 48 km/hr. Find the number of kilometres of good surface. (Form an algebraic equation and solve it).

good road ---- x km

poor road ----- 48-x km

time on good road = x/72
time on poor road = (48-x)/48

x/72 + (48-x)/48 = 3/4
times 144 , the LCD
2x + 3(48-x) = 108

carry on, easy from here