we know that
The area of a rectangle is equal to
where
L is the length side of the rectangle
W is the width side of the rectangle
see the attached figure with letters to better understand the problem
The area of the pool's border is equal to the area of rectangle ABCD minus the area of rectangle EFGH
The formula to calculate the distance between two points is equal to

Step 1
<u>Find the distance AB</u>
Let

substitute the values in the formula




Step 2
<u>Find the distance BC</u>
Let

substitute the values in the formula




Step 3
<u>Find the distance EF</u>
Let

substitute the values in the formula




Step 4
<u>Find the distance FG</u>
Let

substitute the values in the formula




Step 5
<u>Find the area of the pool's border</u>
The area of the pool's border is equal to the area of rectangle ABCD minus the area of rectangle EFGH
<u>Area of the rectangle ABCD</u>

<u>Area of the rectangle EFGH</u>

<u>Area of the pool's border</u>

therefore
<u>the answer is</u>
