Hi Chris -
A quadratic function is simply a parabola. Imagine a parabola on a graph that points either up or down. Now split it in half with the line x=3.
The vertex form of a parabola that points up or down is:
y = a(x-h)^2 + k, where (h,k) is the vertex.
The axis of symmetry (x=3) must pass directly through the vertex. Therefore, the general solution to your problem is:
y = a(x-3)^2 + k
Any real number values for a or k will work. Try it out using some values for a and k (both negative and positive). Graph it and see if you get a parabola that is symmetric with x=3.
Hope this helped