25.5 x 8/100= 2.04
total cost 25.5+2.04= 27.45
Do you want me to divide that? I will answer in comments if so.
You have to organize the parameters of the real-world situation that is known and unknown. Also, you have to distinguish which of them are dependent and independent. Next, you assign letters as your variables. Lastly, you make an algebraic expression by translating the relationship into the mathematics.
You are correct. You multiply both sides of the second equation by -9 so that the y turns into -9y. That way you add it to the +9y in the first equation to get 0y (the y terms cancel afterward). Nice work.