The production of oranges and grapefruit (in millions of tons) in the U.S. for the years 2000 through 2006 is modeled by the polynomial functions below. The variable x represents the number of years since 2000.

Oranges f(x) = -0.044x³+0.258x²-0.657x + 12.883 Grapefruit g(x) = 0.004.x³ - 0.065x² -0.040x + 2.695

What polynomial function is a model for the combined production of oranges and grapefruit in the United States for the years 2000-2006?​