(624 + 158) + 42 = 824
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}624\\ 158\end{array}}\\ \begin{array}{r}782\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}782\\ 42\end{array}}\\ \begin{array}{r}824\end{array}\end{array}$
(396 + 121) + 439 = 956
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}396\\ 121\end{array}}\\ \begin{array}{r}517\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}517\\ 439\end{array}}\\ \begin{array}{r}956\end{array}\end{array}$
Проверка вычислений:
(624 + 158) + 42 = 624 + (158 + 42) = 824
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}158\\ 42\end{array}}\\ \begin{array}{r}200\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}624\\ 200\end{array}}\\ \begin{array}{r}824\end{array}\end{array}$
(396 + 121) + 439 = 396 + (121 + 439) = 956
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}121\\ 439\end{array}}\\ \begin{array}{r}560\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}396\\ 560\end{array}}\\ \begin{array}{r}956\end{array}\end{array}$