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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

It will take luis 18 hours

Step-by-step explanation:

1/a + 1/b = 1 / t

where a is the time for one individual working alone

b is the time the second individual working alone

t is the time the two individuals working together

let a = time for tran to work

b = time for luis to work

1/9 + 1/b = 1/6

multiply by 36b to clear the fractions

36b * (1/9 + 1/b) = 1/6 * 36b

4b + 36 = 6b

subtract 4b from each side

36 = 2b

divide by 2

18 = b

It will take luis 18 hours