The perimeter of a rectangle is calculated by:
[tex]\boxed{P=width +width+length+ length}[/tex]
Remember: In a rectangle, opposite sides are equals.
If we know how much is the width, then it's just apply it to the expression:
[tex]P=width+width+length+length\\312 =68 + 68 + length + length\\312 = 136+(2\cdot length)\\312 - 136 = 2\cdot length\\2\cdot length = 176\\length = \frac{176}{2} \\length = 88[/tex]
Therefore, the length of the pool is 88m.
