Is (1,1),(-4,-2) a function? What is the domain and range?

How to solve a simultaneous equation involved with fractions?

Ineed in figuring out this problem.

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