The function g tells us the amount of remaining water.
The variable x gives us how much time has passed.
Given g(840) = 0,
We can see that the variable x is 840 and the functional value of g is 0.
This means at after 840 minutes the amount of water in the pool will be zero.
Looking at the choices, the correct answer is >>>
After 840 minutes, the pool is empty.