A firm produces tables and bookshelves. Each table yields a profit of $9 and the bookshelves yield a profit of $12. Each week the firm has 12 gallons of varnish and 16 lengths of redwood. The table requires 1 gallon of varnish and 1 length of redwood. Each bookshelf requires 1 gallon of varnish and 2 lengths of redwood.