To find the length of the unknown side \( a \) in the right triangle with the other two sides being 14 ft and 7 ft, we can use the Pythagorean theorem, which states:
\[ a^2 + b^2 = c^2 \]
where \( c \) is the hypotenuse.
Assuming \( 14 \) ft is the hypotenuse, and \( 7 \) ft is one of the legs, we can substitute:
\[ 7^2 + a^2 = 14^2 \]
Calculating \( 7^2 \) and \( 14^2 \):
\[ 49 + a^2 = 196 \]
Subtract \( 49 \) from both sides:
\[ a^2 = 196 - 49 \] \[ a^2 = 147 \]
Taking the square root of both sides to find \( a \):
\[ a = \sqrt{147} \]
Thus, the length of the unknown side \( a \) is:
\[ \sqrt{147} \text{ ft.} \]
So the correct response is:
\(\sqrt{147} \text{ ft.}\)