The Solution:
Given:
The perimeter of a rectangle is 84.
We are asked to find the dimensions ( that is, length and width) of the rectangle.
Let the length of the rectangle be L and W for the width.
So,

By formula, the perimeter of a rectangle is:

Substitute these values in the formula, we get:

Dividing both sides by 2, we get:

Cross multiplying, we get:

Dividing both sides by 7, we get:

To find the length L, we shall put 12 for W.

Therefore, the dimensions of the rectangle is 30 by 12.
Length = 30 units
Width = 12 units