A small purse manufacturer has a single machine that makes the metal parts of a purse. This takes 2 minutes. Another single machine makes the cloth parts in 3 minutes. Then it takes a worker 4 minutes to sew the cloth and metal parts together. Only one worker has the skill to do this. How long will it take to make 6 purses? Answer is 27 minutes, but I don't really see where they get that. I made my pert diagram and got 7 minutes to make a single purse. Then I multiplied that by 6... which would give me 42 minutes. Please show and explain the way to solve this problem.