18. The production function for a candy manufacturer is f(x, y) = 4x + xy + 2√y where x is the number of units of labor and y is the number of units of capital. Assume that the total amount available for labor and capital is 2000, and that units of labor and capital cost 20 and 4, respectively. Find the maximum production level for this manufacturer. (A) 13,844.2 (B)12,425.5 (C)13,201.8 (D)11,392.7