The choi family and the wright family each used their sprinklers last summer. the choi family's sprinkler was used for 15 hours. the wright family's sprinkler was used for 30 hours. there was a combined total output of 1350l of water. what was the water output rate for each sprinkler if the sum of the two rates was 65l per hour?

15c +30w = 1350 . . . . . . combined total output
c +w = 65 . . . . . . . . . . . . total rate

Subtract 15 times the second equation from the first.
(15c +30w) -15(c +w) = (1350) -15(65)
15w = 375 . . . . . . . . simplify
w = 25 . . . . . . . . . . . divide by 15
c = 65 -25 = 40 . . . use the second equation to find c

The Choi family sprinkler had a water output of 40 L/h.
The Wright family sprinkler had a water output of 25 L/h.

The correct answer would be "convenience"