Annabelle and her children went into a movie theater where they sell drinks for $6 each and pretzels for $3.75 each. Annabelle has $75 to spend and must buy no less than 15 drinks and pretzels altogether. Also, she must buy no less than 4 drinks. If xx represents the number of drinks purchased and yy represents the number of pretzels purchased, write and solve a system of inequalities graphically and determine one possible solution.