Bata Aerobics manufactures two models of steppers used for aerobic exercises, x number of luxury models and y number of standard models. Manufacturing each luxury model requires 10 lb of plastic and 10 min of labor. Manufacturing each standard model requires 16 lb of plastic and 8 min of labor. The profit for each luxury model is $50, and the profit for each standard model is $20. If 6000 lb of plastic and 60 labor-hours are available for the production of the steppers per day, how many steppers of each model should Bata produce each day in order to maximize its profit?