A can do a particular work in 6 days . B can do the same work in 8 days. A and B signed to do it for Rs. 3520. They completed the work in 3 days with the help of C. How much is to be paid to C?  Pick one:
A) s . 380	B) s . 600	C) s . 420	D) s . 440	E) s . 480

Rationale: "explanation : amount of work a can do in 1 day = 1 / 6 amount of work b can do in 1 day = 1 / 8 amount of work a + b can do in 1 day = 1 / 6 + 1 / 8 = 7 / 24 amount of work a + b + c can do = 1 / 3 amount of work c can do in 1 day = 1 / 3 - 7 / 24 = 1 / 24 work a can do in 1 day : work b can do in 1 day : work c can do in 1 day = 1 / 6 : 1 / 8 : 1 / 24 = 4 : 3 : 1 amount to be paid to c = 3520 × ( 1 / 8 ) = 440 answer : option d"
Answer: D