Suppose that x thousand units of a commodity can be sold weekly when the price is p dollars per unit and that x and p satisfy the demand equation p + 2x + xp = 38. How fast are weekly sales changing at a time when x = 4, p = 6, and the price is rising at the rate of $.40 per week? O Weekly sales are falling at the rate of 250 units per week. O Weekly sales are falling at the rate 0.25 per week O Weekly sales are rising at the rate of 0.25 units per week. O Weekly sales are rising at the rate of 250 units per week.