To find the height \( h \) of the square pyramid, we can use the Pythagorean theorem.
We have a right triangle formed by:
- The height \( h \) from the vertex to the center of the base.
- The half of the base length which is \( \frac{40 , \text{feet}}{2} = 20 , \text{feet} \).
- The slant height \( s = 25 , \text{feet} \).
According to the Pythagorean theorem:
\[ s^2 = h^2 + \left( \frac{\text{base edge}}{2} \right)^2 \]
Plugging in the values we have:
\[ 25^2 = h^2 + 20^2 \]
Calculating the squares:
\[ 625 = h^2 + 400 \]
Now, subtract \( 400 \) from both sides:
\[ 625 - 400 = h^2 \]
\[ 225 = h^2 \]
To find \( h \), take the square root of both sides:
\[ h = \sqrt{225} = 15 \]
Thus, the height \( h \) of the square pyramid is:
\[ \boxed{15.0 \text{ feet}} \]