Вот подробное решение заданий:
1) \( \frac{7}{40} - \frac{5}{40} = \frac{7-5}{40} = \frac{2}{40} = \frac{1}{20} \).
2) \( \frac{7}{40} + \frac{15}{40} = \frac{7+15}{40} = \frac{22}{40} = \frac{11}{20} \).
3) \( 6 \frac{15}{7} + 2 \frac{9}{7} = 6 + \frac{15}{7} + 2 + \frac{9}{7} = 8 + \frac{15+9}{7} = 8 + \frac{24}{7} = 8 + 3 \frac{3}{7} = 11 \frac{3}{7} \).
4) \( 5 \frac{6}{9} - 3 \frac{2}{9} = 5 + \frac{6}{9} - 3 - \frac{2}{9} = 2 + \frac{6-2}{9} = 2 + \frac{4}{9} = 2 \frac{4}{9} \).
Ответы:
1) \( \frac{1}{20} \).
2) \( \frac{11}{20} \).
3) \( 11 \frac{3}{7} \).
4) \( 2 \frac{4}{9} \).