By reducing the selling price of an article by ₹$900$, a profit of $25\%$ turns into a loss of $5\%$. The original selling price of the article (in ₹) is:

Let the cost price ($CP$) of the article be $100\%$.Original selling price ($S{P}_1$) at $25\%$ profit $=125\%$ of $CP$ New selling price ($S{P}_2$) at $5\%$ loss $=95\%$ of $CP$ The difference between the two selling prices is given as ₹$900$:
$$\text{Difference}=125\%-95\%=30\%\text{ of }CP$$
$$30\%\text{ of }CP=900$$
$$CP=\frac{900}{30}\times 100=\text{₹}3,000$$
The original selling price ($S{P}_1$) is:
$$S{P}_1=125\%\text{ of }3000=\frac{125}{100}\times 3000=\text{₹}3,750$$