A car travelling from city A to B takes an hour lesser to cover the

A car travelling from city A to B takes an hour lesser to cover the distance if it moved 10kmph faster. On the other hand it will take an hour more to cover the distance if it moved 6kmph slower. What is the distance between the two cities?
A)150kms
B)180kms
C)360kms
D)120kms

Source: 4gmat


Please explain