quick Calc Equation question

Hello,

I am stuck with this one question, I do not even know how to begin. Any help would be greatly appreciated.

Determine $\displaystyle a$, $\displaystyle b$, $\displaystyle c$ and $\displaystyle d$ so that the graph of $\displaystyle ax^3+bx^2+cx+d$ has a point of inflection at the origin and a relative maximum at the point $\displaystyle (2,4)$.

I know the point of inflection is when the second derivative equals 0 and the max is when the first derivative equals 0, going from negative y values to positive y values. but how do i use that?

Thanks for all your help!