Renu can do a piece of work in 8 days, but with the help of her friend Suma , she can do it in 4 days. In what time Suma can do it alone?  Choose one.
A) 8
B) 12
C) 14
D) 15
E) 17

Rationale: "renu â € ™ s one day â € ™ s work = 1 / 8 suma â € ™ s one day â € ™ s work = 1 / 4 - 1 / 8 = 1 / 8 suma can do it alone in 8 days . answer : a"
Answer: A