Use the parabola tool to graph the quadratic function. f(x)=3x2+6x−24 graph the parabola by first plotting its vertex and then plotting a second point on the parabola.

The x-location of the vertex of ax²+bx+c is x=-b/(2a). For your parabola, that is
    x = -6/(2·3) = -1

The vertex y-value is then
   f(-1) = 3 -6 -24 = -27

When you move 1 unit either side of the vertex, the value of f(x) changes by the coefficient of x², which is +3. Now, you know 
   vertex = (-1, -27)
   another point = (0, -24)