Suppose the cost C(x), to build a football stadium of x thousand square feet is approximated by C(x) = 7,250,000/x + 60. Given the function, we can substitute values for x to determine the cost of a particular size of stadium or we can substitute values for C(x) to determine the number of square feet.
if the cost of the stadium was $8,000, the, we would determine the size of the stadium, x by substituting x $8,000 for C(x). It becomes