Given,
Selling price = ₹13,500
Loss% = 20%
Let the cost price be x.
∴Loss = 20% of x
Selling price = Cost price - Loss
⇒13,500 = x−20100×x
⇒13,500 = x−15x
⇒13,500 = 45x
⇒x = 16,875
Therefore, she bought it for ₹16,875.
So, cost price of the article = ₹16,875
20% of the cost price
=20100×16,875=₹3,375
Net amount = ₹16,875 + ₹3,375 = ₹20,250
So, in order to gain a profit of 20%, she should sell it at ₹20,250.