Rectangle Perimeter: Solve for X When Area = 20 and Height = 4

Look at the following rectangle:

The area of the rectangle is 20.

What is the perimeter of rectangle ABCD?

The area of the rectangle equals its length multiplied by its width:

$S=AB\times AD$

Let's first substitute the data into the formula:

$20=4\times(x+1)$

$20=4x+4$

$20-4=4x$

$16=4x$

$4=x$

Now we can calculate side AB:

$4+1=5$

The perimeter of the rectangle equals the sum of its sides.

Since each pair of opposite sides are equal in a rectangle, we can calculate that:

$AD=BC=4$

$AB=CD=5$

Finally, let's add all the sides together to find the perimeter:

$4+5+4+5=8+10=18$