\[\boxed{\text{6.89.}}\]
\[\textbf{а)}\ 4,27 + (9,38 + 6,73) =\]
\[= (4,27 + 6,73) + 9,38 =\]
\[= 11 + 9,38 = 20,38\ \]
\[\textbf{б)}\ 0,432 + (0,568 + 4,835) =\]
\[= (0,432 + 0,568) + 4,835 =\]
\[= 1 + 4,835 = 5,835\ \]
\[= 17 + 13 = 30\ \]
\[\textbf{г)}\ 25,629 - (4,429 + 8,2) =\]
\[= (25,629 - 4,429) - 8,2 =\]
\[= 21,2 - 8,2 = 13\ \]
\[\textbf{д)}\ (17,508 + 17,976) - 7,508 =\]
\[= (17,508 - 7,508) + 17,976 =\]
\[= 10 + 17,976 = 27,976\ \]
\[\textbf{е)}\ (39,215 + 29,99) - 5,99 =\]
\[= (29,99 - 5,99) + 39,215 =\]
\[= 24 + 39,215 = 63,215\ \]