Suppose that the sales function for a product L has been estimated as:

Q_L=7-1.6P_L-.2P_C+.8P_S+.0005Y+.0004A

Where, Q_L is the quantity of product L demanded, in thousand per month.

P_L is the price of product L, which is currently $15

P_C is the price of product C, which is currently $25;

P_S is the price of product S, which is currently $20;

Y is the level of per capita income, which is currently $20,000; and

A is monthly advertising, which is currently $15,000.

Express the equation for the demand curve for L.