Question

What do I do?

Answer 1

As a start, find the total volume of the pool

Answer 2

LWH?

1274?

Answer 3

So the volume is 1274 cubic feet.
Lets figure out 100% capacity next.

If one cubic foot has 7.48 gallons, how about 1274 cubic feet?

Answer 4

9529.52 @FortyTheRapper

Answer 5

Right, so now we can set up a ratio

100%/9529.52 = 80%/X

After cross multiplying:

100x = (80)(9529.52)

Now we can solve for X, the answer