A salesman’s terms were changed from a flat commission of 5% on all his sales to a fixed ...

A salesman’s terms were changed from a flat commission of 5% on all his sales to a fixed salary of Rs.1000 plus 2.5% commission on all sales exceeding Rs. 4,000. If his remuneration as per new scheme was Rs. 750 more than that by the previous schema, his sales were worth?