You want

You are given \frac{dV}{dt} as 2 cubic feet per minute

and is just the area of the top of the water.

Consider the triangle formed by the top of the pyramid, the midpoint of one of the sides of the base and the center of the base.

We know the length of the bottom is 6 as this is half of 12.

We also know that the smaller triangle formed with the surface of the water is symmetrical to the larger triangle, as 2 angles are the same.

So if the length of the side on the surface of the water is x,

x=3.6

This means that the side lengths of the surface of the water is 2*3.6 = 7.2 feet and the area is = 51.84 square feet

So

=