its a math question

Question

it algebra 2 lesson on work problems 

Jack accepted a job to paint a new house. He calculated that he can complete the job in 30 hours. He hired a trainee to assist him. He has seen the trainee work and estimates that it the trainee working alone would take 45 hours to complete the job. How much time should the two of them working together need to paint the house? (Round your answer to the nearest tenth

Answer 1

Mary, we look at how much gets done each hour

 

1/30 + 1/45 = 1/x

 

Once we find the common denominator, it actually goes away.

 

3x + 2x = 90

5x = 90

x = 18 hours