The answer is 12 scarves.
If the number N of scarves she can make is inversely proportional to the area A of each scarf, then we have equation:
N = x/A,
where x is the total area of the large piece of fabric she uses
First, we need to calculate what is the total area of the large piece of fabric she uses (x):
It is given:
A = 4 square feet
N = 15
If N = x/A, then: x = A * N = 4 * 15 = 60 square feet
Now, we have to calculate the number of scarves she can make if the area of the scarf is 5 square feet.
So, it is given:
x = 60 square feet,
A = 5 square feet
If N = x/A, then: N = 60/5 = 12 scarves