Two pipes fill the pool in 2 hours 56 minutes, and one first pipe fills the pool in 11 hours.

Two pipes fill the pool in 2 hours 56 minutes, and one first pipe fills the pool in 11 hours. How many hours does one second pipe fill the pool?

Let x be the capacity of the first pipe, then y is the second pipe. The volume of the pool (work performed) is taken as a unit. Let’s compose and solve the equation:
Let’s translate into hours:
2 hours 56 minutes = 2.93 (3) hours
1 / x + 1 / y = 1 / 3.75 = 264/90
By hypothesis 1 / x = 1/11, where x = 11. Substitute in the first equation:
1/11 + 1 / y = 1/264/90
264y – 2904y = -2904
-2640y = -2904
y = 1.1
Answer: one second pipe will fill the pool in 1.1 hours.