A car travels one-third of the way plus 75 kilometers. If it exceeds the midpoint of 15 kilometers, the whole way is one-third of the way plus 60 kilometers, then two-thirds of the way is 60 kilometers, and then the whole way is 90 kilometers.

The formula is (75-15)/(1-1/3) = 90.

Alternatively, the equation can be set to x=90 with the whole distance x km x/3+75=x+ 15.