Machines X and Y produce bottles at their respective constant rates. Machine X produces k bottles in 3 hours and machine Y produces k bottles in 2 hours. How many hours does it take machines X and Y , working simultaneously , to produce 12k bottles?
Options
A) 16
B) 20
C) 15
D) 72 / 5
E) 24

Rationale: x rate = k / 3 y rate = k / 2 k / 3 + k / 2 = 12 k / t solving t = 72 / 5 answer d
Answer: D