Claires backyard is in the shape of a rectangle and has a length of 19.5 feet . it cost her $945.00 to fence in the yard. if fencing cost $15.00 per foot, what is the width of claires backyard? explain how to solve it

You need to know the formula for the perimeter of a rectangle. We won't use it right away, but it is pertinent information.
P = 2 ( l + w )
Now, we know that the fencing costs $15.00 per foot, and that the length is 19.50 feet.
We first need to find the price of one "length" side of the fence.
To do this, multiply 19.50 by 15.00
19.50 x 15.00 = 292.5
Next, we look at the perimeter equation to see what we can plug in where.
P = 2 ( l + w )
We can put in the total price of the fencing for the yard as P, and the amount of one length side of the fence as l.
945.00 = 2 ( 292.5 + w )
And now, we simply solve for w.
945.00 ÷ 2 = ( 2 ( 292.5 + w ) ) ÷ 2
472.5 = 292.5 + w
472.5 - 292.5 = 292.5 + w - 292.5
w = 180
It costs $180 for one "width" side of the fence.
To find out how many feet that is, we do the opposite of what we did with the length. Instead of multiplying by $15.00, we divide by $15.00
$180.00 ÷ $15.00 = 12
The width of Claire's backyard is 12 feet.