6. [2 points] When a homeowner regularly paints their house's exterior, it increases the lifespan of the house's wood shingles. It also increases the value of neighbouring houses. In a particular postal code, each year 10% of homeowners paint their house's exterior. Based on this information and under standard assumptions, surplus is maximized when in the postal code are painted each year. A. more than 10% of houses B. 10% of houses C. less than 10% of houses D. a fraction of houses that may be more or less than 10% of houses