The correct response is:
Rosanna mistakenly added the squared hypotenuse with the square of the longest leg instead of adding both squared legs.
In the Pythagorean Theorem, the correct formula is \( c^2 = a^2 + b^2 \), where \( c \) is the hypotenuse and \( a \) and \( b \) are the lengths of the other two sides. If she calculates \( c \) incorrectly, it could be due to not correctly applying this formula.