How do you know if it is a function

Write numerical coefficient of y² in the expression 2x² - 15xy – 7y²

Cody was 165cm tall on the first day of school this year, which was 10% taller than he was on the first day of school last year.

Acertain drug is made from only two ingredients: compound a and compound b. there are 3 millimeters of compound a used for every 4 millimeters of compound b. if a chemist wants to make 693 milliliters of the drug, how many milliliters of compound a are needed?