\[\boxed{\mathbf{30.}}\]
\[\textbf{а)}\ 32 + 15 = 47\]
\[61 - 40 = 21\]
\[43 + 5 = 48\]
\[73 + 0 = 73\]
\[84 - 3 = 81\]
\[56 - 0 = 56\]
\[\textbf{б)}\ 48 - 7 + 14 = 41 + 14 = 55\]
\[61 + 2 - 13 = 63 - 13 = 50\]
\[75 - 71 + 50 = 4 + 50 = 54\]
\[38 + 0 - 35 = 38 - 35 = 3\]
\[45 - 45 + 28 = 0 + 28 = 28\]
\[6 + 32 - 0 = 38\]