A contractor is calculating the number of decorative stones for a new rectangular patio. The bids always include a count for the number of stones for the edging, E(x), and the number of stones for the center of the patio, C(x). The various patio sizes have lengths represented by the function f(x) and widths represented by g(x). Which statement describes the combined functions E(x) and C(x)? The number of edge stones needed has a constant rate of change, but the number of stones for the center does not. The number of stones for the center has a constant rate of change but the number of edge stones needed does not. Both the number of stones needed for the edge and the number of stones for the center have a constant rate of change. Neither the number of stones needed for the edge nor the number of stones for the center has a constant rate of change