To find the length of the hypotenuse \( c \) in a right triangle with legs \( a \) and \( b \), you can use the Pythagorean theorem, which states:
\[ c^2 = a^2 + b^2 \]
Substituting the given values of \( a \) and \( b \):
\[ c^2 = (5.9)^2 + (6.9)^2 \]
Calculating \( (5.9)^2 \):
\[ (5.9)^2 = 34.81 \]
Calculating \( (6.9)^2 \):
\[ (6.9)^2 = 47.61 \]
Now, add these two results:
\[ c^2 = 34.81 + 47.61 = 82.42 \]
To find \( c \), take the square root of \( c^2 \):
\[ c = \sqrt{82.42} \approx 9.1 \]
Therefore, the length of the hypotenuse \( c \) is approximately:
\[ \boxed{9.1} \text{ feet} \]