\[\boxed{\mathbf{363.}}\]
\[\textbf{а)}\ 398 + 109 = 507\]
\[642 - 256 = 386\]
\[541 - 308 = 233\]
\[420 - 147 = 273\]
\[835 - 475 = 360\]
\[503 + 397 = 900\]
\[\textbf{б)}\ 723 - (546 - 40) =\]
\[= 723 - 506 = 217\]
\[289 + 343 - 600 =\]
\[= 632 - 600 = 32\]
\[916 - (150 + 7) =\]
\[= 916 - 157 = 759\]