The vertex of the parabola is at the point (2,4), and the point (3,6) is on the parabola. what is the equation of the parabola?

We know that for the parent function
  y = x²
when x=1, the value of y is also 1.
That is, when the horizontal distance from the vertex is 1, the vertical distance is also 1.
In your parabola, the point (3, 6) has a horizontal distance of 1 from the vertex (2, 4), but a vertical distance of 2. That means the vertical scale factor is 2, and the translated parabola's equation is ...
  B.  y = 2(x - 2)² + 4

Are you trying to figure out the volume?