Решение:
\begin{aligned}
&2 + 7 = 9 \implies 7 + 2 = 9 \implies 9 - 2 = 7 \implies 9 - 7 = 2 \\
&1 + 6 = 7 \implies 6 + 1 = 7 \implies 7 - 1 = 6 \implies 7 - 6 = 1
\end{aligned}
Ответ:
\begin{aligned}
&2 + 7 = 9 \\
&7 + 2 = 9 \\
&9 - 2 = 7 \\
&9 - 7 = 2
\end{aligned}
\begin{aligned}
&1 + 6 = 7 \\
&6 + 1 = 7 \\
&7 - 1 = 6 \\
&7 - 6 = 1
\end{aligned}