x = longest side , y = middle side , z = shortest side
P = x + y + z
P = 82
x = 2z + 7
y = z + 15
82 = (2z + 7) + (z + 15) + z...combine like terms
82 = 4z + 22
82 - 22 = 4z
60 = 4z
60/4 = z
15 = z
so the shortest side (z) is 15 cm
the second side (y) is : z + 15......15 + 15 = 30 cm
and the longest side (x) is : 2z + 7.....2(15) + 7 = 37 cm