GMAT Problem Solving (PS) | Re: Machine A can produce toys at a constant rate of 2 units per hour and

Machine A can produce toys at a constant rate of 2 units per hour and machine B can produce toys at a constant rate of 5 units per hour. If at least one of either machine A or machine B produces toys, what is the greatest possible hours when machine A and machine B work together at their constant rates so that two machines, A and B, can produce 88 units of toys in 20 hours?

A. 5hrs    
B. 6hrs    
C. 7hrs    
D. 8hrs    
E. 9hrs