Please some body help me

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

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=

Write an algebraic expression to match each statement a. four less than 8 times a number b. twice the difference of a number and six c. nine from a number squared