You can
put this solution on YOUR website!Is it a square base?? If not, then the answer cannot be uniquely determined.
V= LWH, where H=4 feet
1000 = 4 LW
Solve for LW by dividing both sides by 4, so
LW = 250.
The length times width must be such that the product of these is 250. If it is a square base, then

, so

or approximately 15 or 16 feet.
If the dimensions are to come out an even number of feet, the next number less than 15 that divides evenly into 250 is 10, which would be 10 feet by 25 feet. There are many other possibilities. Whatever, it's a BIG tub!!
R^2 at SCC