The length of a rectangle is three times its width. If the perimeter is 84 meters. Find the length of the rectangle

Given: The length of a rectangle is three times its width, perimeter is 84 meters

To find : Length of rectangle

Solution: 

Let the width be x

So length will be 3x 

Perimeter of Rectangle = 2( l + b)

2(x+3x) = 84

2x + 6x = 84

8x = 84

x = 10.5m 

Width =x = 10.5 m

Length = 3 $\times$ 10.5 = 31.5m