We are given that the perimeter of a square is 68. Since the perimeter of a figure is the sum of all of its sides then the formula for the perimeter of a square is:

Where "l" is the length of its sides. We can solve for "l" by dividing both sides by 4:

Replacing the value of the perimeter:

Now, the length of the diagonal of a square is:
![d=\sqrt[]{2}l](https://img.qammunity.org/2023/formulas/mathematics/college/w0uqxox2wb6ihtteqpv6qvluxi54i6bbxw.png)
Replacing the value of "l":
![d=(\sqrt[]{2})(17)](https://img.qammunity.org/2023/formulas/mathematics/college/n6lxrdue91w8akyllqkgusn82kbs59vdeb.png)
Solving the operations:

Therefore, the length of the diagonal is 24 feet.