formula

$T3=T2 \times T1 = \left( \begin{array}{cc} 1 & 3 \\ 2 & 4 \\ \end{array} \right) \times \left( \begin{array}{cc} 5 & 7 \\ 6 & 8 \\ \end{array} \right) =\left( \begin{array}{cc} 19 & 43 \\ 22 & 50 \\ \end{array} \right)$