We have to assume that the perimeter of the pool is 54 feet.
P = 2(length + width)
54 ft = 2((2*width - 3 ft) + width) . . . . . substitute the given information
54 ft = 6*width -6 ft . . . . . . . . . . . . . . . simplify
60 ft = 6*width . . . . . . . . . . . . . . . . . . . add 6 ft
10 ft = width . . . . . . . . . . . . . . . . . . . . .divide by 6
length = 2*(10 ft) - 3 ft = 17 ft . . . . use the relation between length and width
The pool is 17 ft long by 10 ft wide.
