Find the matrix $A$ of the linear transformation $$T(M)= \left[\begin{array}{cc} 2 &6\cr 0 &3 \end{array}\right] M$$ from $U^{2\times 2}$ to $U^{2\times 2}$ (upper triangular matrices) with respect to the basis $$\left\lbrace \left[\begin{array}{cc} 1 &0\cr 0 &0 \end{array}\right], \left[\begin{array}{cc} 1 &1\cr 0 &0 \end{array}\right], \left[\begin{array}{cc} 0 &0\cr 0 &1 \end{array}\right] \right\rbrace$$
$A=$ $\left[\Rule{0pt}{3.6em}{0pt}\right.$$\left]\Rule{0pt}{3.6em}{0pt}\right.$