Iam getting confused right now, can anyone me out? actually find the right answer, !

What is f(3) for the quadratic function f(x)= 2x^2+ + x - 12

Last month, a 770 g box of cereal was sold at a grocery store for $3.10. however, this month, the cereal manufacturer launched the same cereal in a 640 g box, which is being sold at $2.50. what is the percent change in the unit price?

Solve for x. −3/4(x+2)=6 enter your answer in the box