The pool is a box shape with width, length and depth. The volumen of the pool is:
[tex]\text{Volumen}=\text{width}\cdot\text{length}\cdot\text{depth}[/tex]And the area is 761.76 square feet:
[tex]\text{Area}=\text{width}\cdot\text{length}=761.76ft^2[/tex]We also know the width is triple of depth and length is double of width, so:
[tex]\begin{gathered} length=2\cdot\text{width} \\ \text{width}=3\cdot\text{depth}\Rightarrow\text{length}=2\cdot3\cdot\text{depth}=6\cdot\text{depth} \\ \text{Area}=761.76ft^2=width\cdot length=3\cdot depth\cdot6depth \\ 761.76=18\cdot depth^2 \\ depth^2=\frac{761.76}{18}=42.32\Rightarrow depth=\sqrt[]{42.32}\approx6.5\text{ ft} \end{gathered}[/tex]Now, we know the value of depth, so the width and length too.
So, we calculate the volumen:
[tex]\begin{gathered} \text{depth}=6.5ft \\ \text{width}=3\cdot\text{depth}=3\cdot6.5ft=19.5ft \\ \text{length}=2\cdot\text{width}=2\cdot19.5ft=39ft \\ \text{Volumen}=\text{width}\cdot\text{length}\cdot\text{depth}=19.5\cdot39\cdot6.5=4943.25ft^3 \end{gathered}[/tex]The Volumen is 4943.25 cubic feet