Find the sides of the shapes

Question

A regular octagon, a square and an equilateral triangle all have equal sides. If the sum of the perimeters of the square and triangle is no more than 28 cm less than twice the perimeter of the octagon, what is the minimum length of each side.

Answer 1

n=the length of any side of any one of the shapes

4n+3n≤2(8n)-28

7n≤16n-28

7n-16n≤-28

-9n≤-28

9n≥28

n≥28/9

n≥3 1/9 cm is the minimum length