start solving the sum of fractions that is inside the parentheses
[tex]\begin{gathered} \frac{9}{10}-(\frac{1\cdot2+5\cdot1}{5\cdot2}) \\ \frac{9}{10}-\frac{2+5}{10} \\ \frac{9}{10}-\frac{7}{10} \end{gathered}[/tex]then, solve subtraction of fractions with a common denominator
[tex]\begin{gathered} \frac{9-7}{10} \\ \frac{2}{10} \end{gathered}[/tex]simplify
[tex]\frac{2}{10}=\frac{1}{5}[/tex]