420 * 8 = 3360
$\begin{array}{r}\times \underset{¯}{\begin{array}{r}420\\ 8\end{array}}\\ 3360\end{array}$
 
390 * 3 = 1170
$\begin{array}{r}\times \underset{¯}{\begin{array}{r}390\\ 3\end{array}}\\ 1170\end{array}$
 
4700 * 5 = 23500
$\begin{array}{r}\times \underset{¯}{\begin{array}{r}4700\\ 5\end{array}}\\ 23500\end{array}$
 
6800 * 6 = 40800
$\begin{array}{r}\times \underset{¯}{\begin{array}{r}6800\\ 6\end{array}}\\ 40800\end{array}$
 
30700 * 9 = 276300
$\begin{array}{r}\times \underset{¯}{\begin{array}{r}30700\\ 9\end{array}}\\ 276300\end{array}$
 
20080 * 7 = 140560
$\begin{array}{r}\times \underset{¯}{\begin{array}{r}20080\\ 7\end{array}}\\ 140560\end{array}$
 
500 − 786 * 4 = 5000 − 3144 = 1856
$\begin{array}{r}\times \underset{¯}{\begin{array}{r}786\\ 4\end{array}}\\ 3144\end{array}$
 
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}500\\ 3144\end{array}}\\ \begin{array}{r}1856\end{array}\end{array}$
 
4329 + 932 * 8 = 4329 + 7456 = 11785
$\begin{array}{r}\times \underset{¯}{\begin{array}{r}932\\ 8\end{array}}\\ 7456\end{array}$
 
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}4329\\ 7456\end{array}}\\ \begin{array}{r}11785\end{array}\end{array}$