Dadas as matrizes A[tex] \left[\begin{array}{ccc}2&-4\\6&2\\\end{array}\right] B [/tex][tex] \left[\begin{array}{ccc}3&-6\\-3&0\\\end{array}\right] [/tex] E c[tex] \left[\begin{array}{ccc}-1&0\\2&-3\\\end{array}\right] [/tex], sendo a matriz M=3A - 2b +c, a soma dos elementos da diagonal principal da matriz M é: