\[\boxed{\text{6.243.}}\]
\[\textbf{а)}\ 47,8 - 13,43 - m =\]
\[= 34,37 - m\text{.\ }\]
\[m = 2,75:\ \]
\[34,37 - m = 34,37 - 2,75 =\]
\[= 31,62.\ \]
\[\textbf{б)}\ 28,6 + k + 4,6 = 33,2 + k\text{.\ }\]
\[k = 3,6:\ \]
\[33,2 + k = 33,2 + 3,6 = 36,8.\ \]