Question 1011216
If we call the longest side, x, then the other sides are x-15 and x-6.  
We add them together to get 102, or
x + x-15 + x-6 = 102
3x - 21 = 102
3x = 123
x = 41
x-15 = 26
x-6 = 35
So the sides are 41 feet, 35 feet, and 26 feet.