\[\boxed{\mathbf{30.}}\]
\[\textbf{а)}\ 6 \cdot 4 = 24\]
\[6 \cdot 6 = 36\]
\[6 \cdot 8 = 48\]
\[5 \cdot 6 - 3 = 30 - 3 = 27\]
\[3 \cdot 7 - 2 = 21 - 2 = 19\]
\[5 + 2 \cdot 9 = 5 + 18 = 23\]
\[\textbf{б)}\ 60 - 4 \cdot 7 = 60 - 28 = 32\]
\[3 \cdot 9 + 35 = 27 + 35 = 62\]
\[61 - 6 \cdot 9 = 61 - 54 = 7\]
\[24\ :4 \cdot 7 = 6 \cdot 7 = 42\]
\[30\ :5 \cdot 8 = 6 \cdot 8 = 48\]
\[3 \cdot 8\ :6 = 24\ :6 = 4\]