Please help me compute for the additional profit. What would be the equation or formula?

Question

A store owner average day sales of $500, realizing a profit of the selling price. To increase the volume of his sale, he advertised his goods spending an average of $20 a day for advertising. If his average daily sales rose to $700 and the rate of profit remained the same, how much additional product did the advertising bring?

Answer 1

It seems that $20 of advertising resulted in $200 of additional sales revenue. I am not sure what you want here, because the situation seems obvious.