Answer:
E. 13 1/2
Explanation:
As two machine Y and Z at constant rate is in 3/2 .So if a machine Y is working 3/2 then the rate of other machine Z is 2/3 time take. Y take 9 minutes.So, 9 = (2/3) the time
so T = 9 * 3 / 2
T = 13.5
So option E is true.