\[\boxed{\text{6.74.}}\]
\[\textbf{а)}\ 0,879 + 25,278 = 26,157\ \]
\[\textbf{б)}\ 44,122 + 6,9 = 51,022\ \]
\[\textbf{в)}\ 74,372 + 4,228 = 78,6\]
\[\textbf{г)}\ 12,8099 + 0,45 = 13,2599\]
\[\textbf{д)}\ 6,8 + 1,24 + 0,7 =\]
\[= 8,04 + 0,7 = 8,74\]
\[\textbf{е)}\ 149,85 + 8,3 + 0,223 =\]
\[= 158,15 + 0,223 = 158,373\ \]