$$15\frac{1}{10} - 6\frac{4}{10} = (15 - 6) + (\frac{1}{10} - \frac{4}{10}) = 9 + (\frac{1-4}{10}) = 9 - \frac{3}{10} = 8\frac{7}{10}$$
Ответ: $$8\frac{7}{10}$$