Question

How to find the perimeter

Answer 1

We can only answer this question if we know what shape you are talking about. Is this for a square, a triangle, or what?

Answer 2

You already know the perimeter, it's 18, but you need to find length and width
Perimeter is length + length + width + width, and you know the area which is length times width, so you need to find 2 numbers that multiple to 20 and see if they add up to 18.
Numbers that can multiple to 20 and 1 and 20, 2 and 10, 4 and 5.
If you use the formula for perimeter on 20 and 1 you get 42( 20+20+1+1=42)
,if you use it on 2 and 10 you get 24(10+10+2+2)
,and if you use it on 4 and 5 you get 18 (5+5+4+4),