Question

find the area of a square whose peremeter is 40 cm

Answer 1

$perimeter \: of \: square \: = 4 \times side \\ 40cm = 4 \times side \\ \frac{40}{4} = side \\ 10 = side \\ \\ area \: of \: square \: = side \: \times side \\ = 10 \times 10 \\ 100cm {}^{2}$

Answer 2

let the side of the square be x.
perimeter of square = 4a
40 cm = 4 × x
40/4 = x
10 = x

area of square = side^2
= 10^2 = 100 cm