Question

find the breath of rectangle whose perimeter is3600 and length is 800

Answer 1

2(l+b)= 3600
2(800+b)=3600
1600+2b=3600
2b=2000
b=1000

Answer 2

$2(l + b) = perimeter \\ = > 2(800 + b) = 3600 \\ = > 1600 + 2b = 3600 \\ = > 2b = 3600 - 1600 \\ = > 2b = 2000 \\ = > b = 1000 \: unit$