\[\boxed{\mathbf{20}\mathbf{.}}\]
\[\textbf{а)}\ 26 + 33 - 1 = 59 - 1 = 58\]
\[45 - 14 - 1 = 31 - 1 = 30\]
\[37 - 2 - 10 = 35 - 10 = 25\]
\[56 + 4 - 1 = 60 - 1 = 59\]
\[\textbf{б)}\ 40 - (29 + 3) = 40 - 32 = 8\]
\[55 + (31 - 7) = 55 + 24 = 79\]