Subtract 5z^2-z+3 from 7x^2-4x

With #! i’ve tried to figure it out but i can’t.

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

When i'm with my factor 5, my prodect is 20 .when i'm with my addend 6' my sum is 10.what number am i