Explanation:
2×length + 2×width = 204 cm
length = x
width = 3×(x + 2)
as consecutive even integers are always spaced out by 2 (2, 4, 6, ...).
we are using these 2 equations in the first main equation :
2×x + 2×3×(x + 2) = 204
2x + 6x + 12 = 204
8x + 12 = 204
8x = 192
x = 192/8 = 24
length = x = 24 cm
width = 3(x + 2) = 3×26 = 78 cm