N can do a piece of work in 80 days. He works at it for 10 days and then M lone finishes the remaining work in 42 days. In how much time will N and M, workings together, finish the work?

প্রশ্নঃ N can do a piece of work in 80 days. He works at it for 10 days and then M lone finishes the remaining work in 42 days. In how much time will N and M, workings together, finish the work?