A can do a piece of work in 10 days and B can do it in 15 days and C can do it 20 days. They started the work together and A leaves after 5 days and B leaves after 3 days from the beginning. How long will work lost? Pick.
A) 2	B) 4	C) 5	D) 6	E) 7

Rationale: "5 / 10 + 3 / 15 + x / 20 = 1 x = 18 / 3 = 6 answer : d"
Answer: D