In how many days will the original gang of pipe layers, under the supervision of foreman B, finish the original pipe-laying job?

A gang of pipe layers working under the supervision of foreman A can finish a pipe-laying job in 20 days. The same gang of pipe layers working without the supervision of a foreman can finish the same pipe-laying job in 25 days. The project engineer, desiring to finish the job in 20 days, employed the gang of pipe layers under the supervision of foreman A. However, at the end of the fifth working day, foreman A quit the job.