\[\boxed{\mathbf{5}\mathbf{.}}\]
\[\textbf{а)}\ 45 + 4 = 49\]
\[45 + 6 = 51\]
\[45 - 4 = 41\]
\[45 - 6 = 39\]
\[\textbf{б)}\ 37 + 5 - 30 = 42 - 30 = 12\]
\[64 - 50 + 8 = 14 + 8 = 22\]
\[52 - 14 + 22 = 38 + 22 = 60\]
\[49 + 34 - 13 = 83 - 13 = 70\]