The fence is a 8x4 fence as they multiply up to 32 square feet and 8 is double 4. If you add 8+8+4+4 you will get 24. Then you multiply the perimeter (24) by 3 to get the final cost. This means that the final cost will be $72.00.
The rate for one unit of a given quantity is called a(n) Unit Rate.
20*.4= 8
(20 as the original price, .4 is 40% as a decimal)
20+8
(eight being 40% of 20)
$28 is the new price.