PLEASE HELP ME SOLVETHIS: If A Trader Gains 15% by Selling An Article For $1560.00, What Is The Cost Price
A GAIN of 15% means that the selling price is 115%, or 1.15, which is also represented by $1,560
With cost price being P, and since 100% (cost) is being sought, we set up the following PROPORTION: 
Solve this for P, by first cross-multiplying, to obtain the cost price.
FYI: It's definitely NOT $1,326, according to the other person.