Machines A and B produce bottles at their respective constant rates. Machine A produces k bottles in 2 hours and machine B produces k bottles in 3 hours. How many hours does it take machines A and B , working simultaneously , to produce 15k bottles? Choose one.
A) 10
B) 15
C) 12
D) 30
E) 18
x rate = k/2   y rate = k/3   k/2 + k/3 = 15k / T   solving T = 18   Answer 18
<result>E</result>
Machines A and B produce bottles at their respective constant rates. Machine A produces k bottles in 2 hours and machine B produces k bottles in 3 hours. How many hours does it take machines A and B , working simultaneously , to produce 15k bottles?