\[\boxed{\mathbf{34.}}\]
\[\textbf{а)}\ 30 + 4 - 5 = 34 - 5 = 29\]
\[2 + 40 - 6 = 42 - 6 = 36\]
\[50 - 5 - 7 = 45 - 7 = 38\]
\[71 - 30 - 2 = 41 - 2 = 39\]
\[60 - 5 - 5 = 55 - 5 = 50\]
\[82 - 20 - 3 = 62 - 3 = 59\]
\[\textbf{б)}\ 16 + 35 - 12 = 51 - 12 = 39\]
\[83 - 25 + 13 = 58 + 13 = 71\]
\[3 + 48 - 45 = 51 - 45 = 6\]