A car travels a certain distance taking 7 hrs in forward jou

A car travels a certain distance taking 7 hrs in forward journey, during the return journey increased speed 12km/hr takes the times 5 hrs. What is the distance travelled
(a) 210 kms (b) 30 kms (c) 20 kms (d) none of these   

Solution

Let the speed of the forward journey = x kmph
Time taken for the forward journey = 7 hrs
The speed of the return journey = x+12 kmph
Time taken for the forward journey = 5 hrs
The distance travelled in both ways are equal.
7x = 5(x+12)
7x = 5x+60
7x-5x = 60
2x = 60
x = 60/2 = 30 kmph
The distance travelled = 7x = 7*30 = 210 kms