\[\boxed{\text{6.4.}}\]
\[\textbf{а)}\ 3,7 = 3\frac{7}{10};\ \]
\[\textbf{б)}\ 41,5 = 41\frac{5}{10} = 41\frac{1}{2};\ \]
\[\textbf{в)}\ 567,99 = 567\frac{99}{100};\ \]
\[\textbf{г)}\ 7,003 = 7\frac{3}{1\ 000};\ \]
\[\textbf{д)}\ 87,78 = 87\frac{78}{100} = 87\frac{39}{50};\ \]
\[\textbf{е)}\ 0,32 = \frac{32}{100} = \frac{8}{25};\ \]
\[\textbf{ж)}\ 0,80 = \frac{80}{100} = \frac{8}{10} = \frac{4}{5};\ \]
\[\textbf{з)}\ 0,08 = \frac{8}{100} = \frac{2}{25};\ \]
\[\textbf{и)}\ 0,88 = \frac{88}{100} = \frac{22}{25}\text{.\ \ \ }\]