Let $\displaystyle a_1= \begin{bmatrix} 1 \\ 4 \\ -2 \end{bmatrix}, a_2= \begin{bmatrix} -2 \\ -3 \\ 7 \end{bmatrix}$ and $\displaystyle b= \begin{bmatrix} 4 \\ 1 \\ h \end{bmatrix} $. For what value(s) of h is b in the plane spanned by $\displaystyle a_1 $and $\displaystyle a_2$?