Eduardo has 9/10 hour to finish his math homework. If he finishes 4 1/2 problems, and it takes him an equal amount of time to do each problem, how long does he take to finish one problem?
A. 9/40hour (He finishes 4 1/2 problems, not 4.)
B. 4 1/20 hours
C. 1/5 hour
D. 5 hours (He has less than 1 hour to finish 4 1/2 problems.)