David and his children went into a bakery where they sell donuts for $1.75 each and brownies for $1.25 each. David has $20 to spend and must buy a minimum of 12 donuts and brownies altogether. Also, he must buy a maximum of 4 donuts and a maximum of 12 brownies. If xx represents the number of donuts purchased and yy represents the number of brownies purchased, write and solve a system of inequalities graphically and determine one possible solution.