§ Задание 30
\[\boxed{\mathbf{30}\mathbf{.}}\]

\[\textbf{б)}\ 58 + 21 - 30 = 79 - 30 = 49\]
\[3 + 63 - 40 = 66 - 40 = 26\]
\[92 - (50 - 0) = 92 - 50 = 42\]
\[\boxed{\mathbf{30}\mathbf{.}}\]

\[\textbf{б)}\ 58 + 21 - 30 = 79 - 30 = 49\]
\[3 + 63 - 40 = 66 - 40 = 26\]
\[92 - (50 - 0) = 92 - 50 = 42\]