Zack's locker is half as big as Timothy's locker. Peter's locker is 1/4 as big as Zack's locker. If Peter's locker is 5 cubic inches, how big is Timothy's locker in cubic inches?
Give me a clear explanation. 
Zack's locker is 5*4=20 cubic inches.
Timothy's locker is 20*2=40 cubic inches.