If $\begin {bmatrix} 1 & 2 & x \\ 4 & -1 & 7\\ 2 & 4 & -6\end{bmatrix}$ is a singular matrix, then x is equal to

Question

$$\begin {array} {1 1} (a)\;0 & \quad (b)\;1 \\ (c)\;-3 & \quad (d)\;3 \end {array}$$