Question

Given the perimeter of a rectangle and either the length or​ width, find the unknown measurement using the appropriate formula.

Answer 1

$p = 2l + 2w$
P=Perimeter
L=Length
W=Width

Hints given are P= 76, L=20 so 2L=40

76=40+2w
76-40=2w
36=2w
18=w

Answer 2

The formula of a perimeter of a rectangle:

P = 2(w + l)

We have P = 76 cm and l = 20 cm.

Substitute:

2(w + 20) = 76       use distributive property

(2)(w) + (2)(20) = 76

2w + 40 = 76     subtract 40 from both sides

2w = 36       divide both sies by 2

w = 18

Answer: the width = 18 cm