If A, B and C are three singular matrices given by \(A=\left[\begin{array}{ll}1 & 4 \\ 3 & 2 a\end{array}\right], B=\left[\begin{array}{ll}3 b & 5 \\ a & 2\end{array}\right] \)  and \(C=\left[\begin{array}{cc}a+b+c & c+1 \\ a+c & c\end{array}\right] \), then the value of abc is :