#### Answer

$\frac{3}{5}$

#### Work Step by Step

In order to add or subtract fractions, we need common denominators. Because 3/10 and 9/10 already have the same denominator, 10, we can subtract the numerators:
$ \frac{9}{10} - \frac{3}{10} = \frac{6}{10}=\frac{3}{5}$