Find b such that the homogeneous system with augmented matrix below has non-trivial solutions:

$\displaystyle A =

\begin{array}{c}\ \\ \\ \end{array}\;\begin{vmatrix}\;-2 & 4 & -18 & 0\;\\\;-4 & 0 & b & 0\;\\\;2 & 1 & 3 & 0\end{vmatrix}

$

So I know a system of equations is homogeneous if all the constant terms are zero, and I know to make a nontrivial solution I need at least one variable to have a nonzero value.

My question is, what is b supposed to be? Is there a single number that it should end up being? Or can it be 1 or 2 or 3, etc.?