The formula for calculating the perimeter of a rectangle is to add all the sides up.
i.e. P = x + x + y + y
where P = perimeter
x = width
y = length
so to find the dimensions for this rectangle, let the width of the rectangle be x and the length be 3x (since its 3 times the width of the rectangle).
Perimeter = x + x + 3x + 3x
putting the value of perimeter and adding up the sides:
72 = 8x
72/8 = x
x = 9
Now, we have found the width (x) to be 9 so we can find the length too.
length was supposed as 3x
3(x) = 3(9) = 27
so width = 9
and length = 27
