Answer:
If the square then the area = side * side.
A = 50
therefore side = square root of 50
The longest line that fits in a square is a diagonal line from corner to corner. The length of this can be calculated using pythogoras' theorem.
A2 + B2 = C2
For this specific square A = B = squareroot of 50
So 50 + 50 = C2
C2 = 100
C = 10
The longest line is 10 feet