Rate and Time distance

Question

Jason and Damian are looking to complete a slideshow on bats for their class together. Jason would normally take 6 hours to complete the slideshow by himself, and it would take Damian 12 hours to complete the slideshow by himself. Damian starts working on the lesson first and spends 8 hours working on it by himself at which point Jason steps in and helps him work on it. How much longer will it take for them to complete the lesson, now that they are working together?

Answer 1

In 8 hrs Damian will complete 2/3 of the job, leaving 1/3 to be completed by both boys working together.

The joint rate is (1/6) + (1/12); for x hrs to complete 1/3 of the job

x[(1/6)+(1/12)]=3x/12 = 1/3

and x=4/3