Question

22. A and B separately can do a piece of work in 36 days and 20 days respectivel
Both started together. After 9 days Cjoined them and whole work was cor
pleted in 12 days. In how many days can C alone do the same piece of work?
1) 48
2) 60
3) 42
4) 45​

Answer 1

Answer:

3) 42 I can't know it will right or wrong I'm little bit confused.