\[\boxed{\mathbf{17.}}\]
\[\textbf{а)}\ 45 + 3 = 48\]
\[56 - 2 = 54\]
\[61 + 4 = 65\]
\[4 + 42 = 46\]
\[64 - 2 = 62\]
\[7 + 31 = 38\]
\[6 + 22 = 28\]
\[49 - 5 = 44\]
\[55 - 4 = 51\]
\[\textbf{б)}\ 50 + (11 - 9) = 50 + 2 = 52\]
\[(12 - 7) + 31 = 5 + 31 = 36\]
\[44 + (13 - 8) = 44 + 5 = 49\]