Question

find the length of the rectangle whose perimeter is 56cm and width is 7cm

Answer 1

perimeter=56 cm
width(breadth)= 7cm
perimeter=2(l+b)

putting values in 2(l+b)
56= 2(l+7)
56=2l+14
56-14=2l
42=2l
42/2=l
l= 21cm
Ans:- length(l)=21cm

Answer 2

$let \: length \: be \: x \\ \ \\ perimeter \: = 2(l + b) \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = 2x + 14 \\ \: \: \: \: \: \: \: \: \: \: \: 56 = 2x + 14 \\ \: \: \: \: \: \: \: \: \: \: 56 - 14 = 2x \\ \: \: \: \: \: \: \: \: \: \: \: x = 42 \div 2 = 21 \\ hence \: length \: = 21cm \\ hope \: this \: will \: help \: u$