Answer:
The rug should be 15 ft wide and 28 ft long.
Step-by-step explanation:
I have attached a figure that represents the situation.
The the rug is
by
, the width of the strip of floor is
.
We are told that Cynthia can only afford 420 square feet of carpeting; therefore, it must be that
<em>(this says the area of the rug must be 420 square feet)</em>
From the figure we see that


Therefore,

We expand this equation and get:

using the quadratic equation we get two solutions:

since the second solution, namely
, is larger than one of the dimensions of the room (is greater than 19 ft) it cannot be the width of the strip; therefore, we take
to be our solution.
Now we find the dimensions of the rug:

The rug is 15 ft wide and 28 ft long.