Answer:
18cm
Explanation:
We have the length of the rectangle but we need to find the width which we'll call w. Area is a, l is length.
a = l * w
20 = 5 * w
divide both sides by 5 to cancel the multiplication by 5 on the right side
4 = w
The rectangle is going to have two sides that are the length of l, and two sides that are the the length of w. We're looking for the perimiter p.
p = 2l + 2w
p = (2 * 5) + (2 * 4)
p = 18