Workers leaving partway through a job

Fifteen workers can complete a job in \(6\) h \(40\) min. All workers work at the same constant rate. Assume that the work can be shared between them without any loss of efficiency and that there are no breaks or other interruptions.

1. Find the time taken by ten workers to complete the job if all ten work throughout.[2]

Instead, ten workers start the job together. After exactly one hour, four of them leave. The remaining six continue until the job is complete.

2. Find the further time needed to complete the job after the four workers leave.[3]
3. Find the total time from the start of the job until it is complete.[1]