A paint company makes two brands of latex paint. Sales figures indicate that if the first brand is sold for x dollars per quart and the second for y dollars per quart, the demand for the first brand will be Q quarts per month, where Q(x, y) = 200 + 10x² − 20y It is estimated that t months from now the price of the first brand will be x(t) = 18 + 0.02t dollars per quart and the price of the second will be y(t) = 21 + 0.4√t dollars per quart. At what rate will the demand for the first brand of paint be changing with respect to time 9 months from now?