algebra word problem

Question

Cora can stuff an a pile of letters in envelopes in 3 hours. Lopes takes 4 hours to do the same job. How long would it take them to do this job if they worked together?

Answer 1

Cora does 1/3 of the job in an hour.

Lopes does 1/4 of the job in an hour

Together they do 7/12 of the job in an hour.

They will do the whole job 12/7 hour