Initially, Lizzy had $30; she loaned out $15 so she has $30-$15 = $<<30-15=15>>15 left
Her friend is returning the $15 with 20% interest for a total of $15+($15*(20/100)) = $<<15+15*(20/100)=18>>18
Lizzy will now have $15+$18 = $<<15+18=33>>33
#### 33