Question

the length of a rectangle is three times its breadth if the perimeter is 84 find the length and breadth of the rectangle
$2(l + b) = perimeter$

Answer 1

2(l+b)=84
2(3x+x)=84
8x=84
x=10.5

hence length=3x=3×10.5=31.5
and breadth=x=10.5

Answer 2

Hello friend☺
$perimeter = 2(length + breadth) \\ let \: the \: beadth \: be \: x \\ then \: length = 3x$
84unit= 2(3x+x)
84 unit/2= 4x
42 unit/4=x
10.5unit= breadth
Length= 3× 10.5=31.5units
Hope it helps