For 6 months, Shara was able to return $10 x 6 = $<<10*6=60>>60 to her brother.
Since she already returned half of the money, then this means she currently owes her brother $<<60=60>>60.
Four months from now, she will be able to pay an additional $10 x 4 = $<<10*4=40>>40.
Thus, she will still owe her brother $60 - $40 = $<<60-40=20>>20 four months from now.
#### 20