To determine the height \( h \) of the square pyramid using the Pythagorean Theorem, we can set up a right triangle involving the slant height, the height, and half the length of the base edge.
- The given information tells us that the slant height (l) is 25 feet and the length of a base edge (b) is 40 feet.
- Half of the base edge \( \left(\frac{b}{2}\right) \) is \( \frac{40}{2} = 20 \) feet.
We can use the Pythagorean theorem, which states that in a right triangle:
\[ l^2 = h^2 + \left(\frac{b}{2}\right)^2 \]
Plugging in the known values:
\[ 25^2 = h^2 + 20^2 \]
Calculating each square:
\[ 625 = h^2 + 400 \]
Next, we solve for \( h^2 \):
\[ h^2 = 625 - 400 \] \[ h^2 = 225 \]
Now, take the square root of both sides to find \( h \):
\[ h = \sqrt{225} = 15 \]
Therefore, the height of the pyramid \( h \) is 15.0 ft. Thus, the correct answer is:
15.0 ft.