When Mr. Ben writes the cheque, he remains with $2000-$600 = $<<2000-600=1400>>1400
His debtor pays him $800, increasing his operation capital to $1400+$800 = $<<1400+800=2200>>2200
He spends $1200, remaining $2200-$1200 = $1000 for business operations cost after maintenance.
#### 1000