Function Notation & Matrices

Today in class we were told to find "f(x)". Since "f(x)" is just another way to say "y", all we had to do was substitute "x" with three since it said: Find f(3). Then we had to simplify all the equations and then multiply after that and then find the determinant. As always, I'm bad at explaining things so here is the problem in all of it's glory:

So after countless and countless attempts to find out this answer, it turned out that Mr. S had to give me the answer. I really hope I'm ready for the test tomorrow. Well, ready for it or not, bring it on!