Two Machines That Fill Cereal Boxes Work at the Same

Multiple Choice

Two machines that fill cereal boxes work at the same rate. After they work for 5 h, one machine breaks down. The second machine requires 10 more hours to finish filling the boxes. How long would it have taken one of the machines, working alone, to fill the boxes?

A) 23 h
B) 21 h
C) 10 h
D) 24 h
E) 20 h