The demand equation for popular ice cream is CX = 20 - 10Px + 0.002I + 20Py, where CX is the monthly consumption of the ice cream of a family in ounces, Px is the price per ounce which is given $4, I is the annual income of the family which is $40,000, Py is the price of competitor brand of ice-cream which is $5. Calculate the monthly consumption of the ice cream (in ounces).