Howard and Edward, working together, can complete a job in 12 hours. Edward requires 18 hours to do this job alone. Howard and Edward start the job. After they worked for 4 hours, Howard left the job. How many hours will Edward require to finish the job working alone?
6 hours is WRONG!!
If both can do the job in 12 hours, then in 4 hours, they will have done:
With of work completed by both, in 4 hours,
With Edward taking 18 hours to do entire job alone, and doing of job in 1 hour, time (T) taken by Edward to complete remaining of job is:
T, or time taken by Edward to complete remaining of job =