\[\boxed{\mathbf{253.}}\]
\[\textbf{а)}\ 314 + 520 = 834\]
\[450 - 120 = 330\]
\[255 + 312 = 567\]
\[463 - 130 = 333\]
\[253 + 116 = 369\]
\[657 - 157 = 500\]
\[\textbf{б)}\ 845 - 0 + 134 =\]
\[= 845 + 134 = 979\]
\[498 - (234 + 141) =\]
\[= 498 - 375 = 123\]
\[570 + (394 - 280) =\]
\[= 570 + 114 = 684\]