side1 + side2 + side 3 = 84
side1 is the shortest side, and its length is x.
side2 is the middle side, and its length is x + 7
side3 is the longest side, and its length is 2x - 7
x + x + 7 + 2x - 7 = 84
4x = 84
x = 21
side1 = x = 21
side2 = x + 7 = 21 + 7 = 28
side3 = 2x - 7 = 2(21) - 7 = 42 - 7 = 35
The length of the sides are 21 m, 28 m, and 35 m.