Equation of a curve and finding the value of k.

Hello, can anyone help me how to find the value of k? I keep getting the wrong answer. I got 4.4 but the correct answer is 9. Here's the question:

The equation of a curve is y=3x^2-kx+2, where k is a constant. The tangent to the curve at the point where x=2 passes through (5,5). Find the value of k.

That's the question.

I did my working like this.. Firstly, I have to find the tangent which I got 12-k. Then I tried to solve everything. I put the coordinates into the equation of a curve.. Which gives me the value of k but I got 4.4 :S