Question 280928
Frank does 1/30th. of the job in 1 hour

Frank and Ed do 1/12Th job in 1 hour

1/12 - 1/30 = part of job done by ed in 1 hour

5-2 / 60 

3/60 = 1/20 th of jon in 1 hour

Ed takes 20 hours to do the job alone