7. \( \frac{3}{7} \cdot\left(\frac{4}{5}-0,35\right) \)

Let's break down the expression inside the parentheses first. We know that \(0.35\) is equivalent to \(\frac{35}{100}\), which simplifies to \(\frac{7}{20}\). Now, converting everything to a common denominator, we rewrite \(\frac{4}{5}\) as \(\frac{16}{20}\). Thus, \[ \frac{4}{5} - 0.35 = \frac{16}{20} - \frac{7}{20} = \frac{9}{20}. \] Now we can substitute this back into the original expression: \[ \frac{3}{7} \cdot \frac{9}{20} = \frac{3 \times 9}{7 \times 20} = \frac{27}{140}. \] Therefore, the final answer is: \[ \frac{27}{140}. \]