On a cold winter day you buy roasted chestnuts from a street vendor. Into the pocket of your down parka you put the change he gives you- coins constituting 9.00 $\mathrm{g}$ of copper at $-12.0^{\circ} \mathrm{C}$ . Your pocket already contains 14.0 $\mathrm{g}$ of sitver coins at $30.0^{\circ} \mathrm{C}$ . A short time later the temperature of the copper coins is $4.00^{\circ} \mathrm{C}$ and is increasing at a rate of $0.500^{\circ} \mathrm{C} / \mathrm{s}$ . At this time, (a) what is the temperature of the silver coins, and (b) at what rate is it changing?