\[\boxed{\mathbf{231.}}\]
\[\textbf{а)}\ 132 + 5 = 137\]
\[364 + 3 = 367\]
\[6 + 231 = 237\]
\[537 - 2 = 535\]
\[716 - 4 = 712\]
\[859 - 5 = 854\]
\[\textbf{б)}\ 868 - 5 + 30 = 863 + 30 =\]
\[= 893\]
\[422 + (307 - 300) = 422 + 7 =\]
\[= 429\]
\[978 - (64 - 58) = 978 - 6 =\]
\[= 972\]