Which is the correct graph for: y= - 4x+3

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?

Damon makes 20 cups of lemonade by mixing lemon juice and water. the ratio of lemon juice to water is shown in the tape diagram. lemon juice\text{lemon juice} lemon juice water\text{water} water how much lemon juice did damon use in the lemonade? cups

Would greatly appreciate these 3 answers