\( \frac{6,8-2\frac{3}{4}}{2\frac{16}{21}+3\frac{2}{3}}=\frac{6,8-2,75}{2\frac{16}{21}+3\frac{2}{3}}=\frac{4,05}{\frac{58}{21}+\frac{11}{3}}=\frac{4,05}{\frac{58+77}{21}}=\frac{4,05}{\frac{135}{21}}=\frac{405}{100}:\frac{135}{21}=\frac{81}{20} \cdot \frac{21}{135}=\frac{27}{20} \cdot \frac{7}{45}=\frac{3}{20} \cdot \frac{7}{5}=\frac{21}{100}=0,21\)
30% от 0,21:
\(0,21 \cdot 0,3 = 0,063\)
Ответ: 0,063