The first two pieces are the same, let each of those equal x, so you have x + x = 2x
The 3rd piece is the sum of the first two + 4, so this would be 2x + 4
Now you have 2x + 2x + 4 = 100 cm
Combine like terms:
4x +4 = 100
Subtract 4 from both sides
4x = 96
Divide both sides by 4
X = 24
First piece is 24 cm
Second piece is 24 cm
Third piece is 52 cm