The demand for good X is estimated to be Qxd = 10,000 - 4Px + 5Py + 2M + Ax, where Px is the price of X, Py is the price of good Y, M is income, and Ax is the amount of advertising on X. Suppose the present price of good X is $50, Py is $100, M is $25,000, and Ax = 1,000 units. What is the own price elasticity of demand for good X?