Together, Tran and Luis take 6 hours to deliver newspapers. If Tran works alone, it takes him 9 hours. How long would it take Luis, working alone, to deliver all the newspapers?

Options:

12 hours

15 hours

18 hours

16 hours

18 hours

Step-by-step explanation:

We work in fractions of the job done per hour.

So in the case of Tran alone he does 1/9 of the job per hour.

We have the equation 1/9 + 1/x = 1/6 where x is the time taken for Luis to deliver the newspapers.

1/9 + 1/x = 1/6

Multiply through by the LCM 18x:-

2x + 18 = 3x

18 = x