Answer:
A. y = x^2 -6x + 13
Step-by-step explanation:
The parabola that opens up and has line of symmetry x=3 and a minimum at x=3 is

The reason is that, we can write this function in the vertex form to get;



Hence the line of symmetry is x=3 and the vertex is (3,4)
I believe the answer you are looking for is the quadratic formula. because it has the formula correct, and it to me just looks exactly like it.
So, it has the ax^2+bx+c=0 but just a little difference, it has a subtracting sign instead of adding.
I don't know if I am right, but that is my guess. I remember doing those lol
Since we are solving for b, you need to get it by itself. So you would divide both sides by 3a. That would leave b= -7/3a.
Hope this helps!!