How to find area of polygon please explain

To find the area of a regular polygon, all you have to do is follow this simple formula: area = 1/2 x perimeter x apothegm. Here is what it means: Perimeter = the sum of the lengths of all the sides. Apothegm = a segment that joins the polygon's center to the midpoint of any side that is perpendicular to that side.

step-by-step explanation:

given perimeter: 28cm

length: 9cm

atp,

2(l+w)=p of the reactangle

2(9+x)=28

18+2x=28

2x=28-18

x=10/2

x=5

therefore width is 5 cm