This fraction

, is not a mixed fraction.

is a mixed fraction.
If 20-2.3=17.7, then if you add 17.7 to 2.3. it equals 20 which is called the communicative property because whatever you add or subtract, the answer is the same
17.7+2.3=2.3+17.7
She played 18 games, so subtract 18 from 40 to get your answer
She did NOT play 22 games
Hope I helped!