§ Задание 19
\[\boxed{\mathbf{19}\mathbf{.}}\]

\[\textbf{б)}\ 62 + 20 - 40 = 82 - 40 = 42\]
\[78 - 3 - 30 = 75 - 30 = 45\]
\[56 + (12 + 8) = 56 + 20 = 76\]
\[89 - (53 - 3) = 89 - 50 = 39\]
\[\boxed{\mathbf{19}\mathbf{.}}\]

\[\textbf{б)}\ 62 + 20 - 40 = 82 - 40 = 42\]
\[78 - 3 - 30 = 75 - 30 = 45\]
\[56 + (12 + 8) = 56 + 20 = 76\]
\[89 - (53 - 3) = 89 - 50 = 39\]