Concept
The angles between the two sides 2ft and 3ft is a right angle, hence we can apply the Pythagoras theorem to find the length of the longest diagonal.
Step 1: Name all the sides
Opposite = 2 ft
Adjacent = 3 ft
Hypotenuse = x ft
Step 2: Apply the Pythagoras theorem below to find x.
Step 3: Final answer
x = 4 is closest ( The answer can also be 3.6 )