AMC 8 1994 Problem 14

Two children at a time can play pairball. For $90$ minutes, with only two children playing at time, five children take turns so that each one plays the same amount of time. The number of minutes each child plays is $\text{(A)}\ 9 \text{(B)}\ 10 \text{(C)}\ 18 \text{(D)}\ 20 \text{(E)}\ 36$