\[\boxed{\mathbf{2.}\mathbf{332}}\]
Пояснение.
Решение.
\[\textbf{а)}\ 40\%\ от\ 30:\]
\[30 \cdot 0,4 = 12.\]
\[\textbf{б)}\ 55\%\ от\ 13,8:\]
\[13,8 \cdot 0,55 = \frac{138 \cdot 55}{10 \cdot 100} =\]
\[= \frac{69 \cdot 11}{100} = \frac{759}{100} = 7,59.\]
\[\textbf{в)}\ 63\%\ от\ \frac{4}{9}:\]
\[\frac{4}{9} \cdot 0,63 = \frac{6}{9} \cdot \frac{63}{100} = \frac{28}{100} = 0,28.\]
\[\textbf{г)}\ 78\%\ от\ 26\frac{1}{3} = \frac{79}{3}:\]
\[\frac{79}{3} \cdot 0,78 = \frac{79}{3} \cdot \frac{78}{100} = \frac{79 \cdot 26}{100} =\]
\[= \frac{2054}{100} = 20,54.\]