Problem Solving

On a staurday night, each of the rooms at a certain motel was rented for either 40$ or 60$. if 10 of the rooms that were rented for 60$ had instead be rented for 40$, then the total rent the motel charged for that night would have been reduced by 25%. what was the total rent the motel actually chraged for that night?

A) 600
B) 800
C) 1000
D) 1600
E) 2400


Does anyone have a fast way to solve this??

Thank you!