Question 557265
rate x time = work

pump A | 1/12 x 7 = 7/12
pump B | 1/x x 7 = 7/x

7/12 + 7/x = 1
LCM = 12x
12x(7/12 + 7/x = 1)
7x + 84 = 12x
84 = 12x - 7x
84 = 5x
84/5 = 5x/5
84/5 minutes or 16 4/5 minutes or 16 minutes and 48 seconds