Exercise $7\mathrm{.}1\mathrm{.}3$: Suggest suitable keys and foreign keys for the relations of the PC database: Product$($maker$,$ model, type$)$ PC$($model$,$ speed, ram, hd$,$ price$)$ Laptop$($model$,$ speed, ram, hd$,$ screen, price$)$ Printer$($model$,$ color, type, price$)$ of Exercise $2\mathrm{.}4\mathrm{.}1.$ Modify your SQL schema from Exercise $2\mathrm{.}3\mathrm{.}1$ to include declarations of these keys.