Let the second side be x inches long, Then:-
first side = 2x and third side = 2x + 7.25 inches long.
therefore:- x + 2x + 2x + 7.25 = 79.75
5x = 79.75 - 7.25 = 72.50
x = 72.50 / 5
= 14.5 ins
So longest side = 2x + 7.25
= 14.5 *2 + 7.25
= 36.25 inches (answer).