Step 1: Understanding Cost Price and Selling Price The Cost Price (CP) is the price at which an item is purchased. The Selling Price (SP) is the price at which the item is sold. Step 2: Identifying the given values \[ CP = Rs. 21000, \quad SP = Rs. 18900. \] Step 3: Calculating Loss Loss occurs if the selling price is less than the cost price: \[ \text{Loss} = CP - SP = 21000 - 18900 = Rs. 2100. \] Step 4: Calculating Loss Percentage Loss percentage is given by: \[ \text{Loss %} = \left( \frac{\text{Loss}}{CP} \right) \times 100 = \left( \frac{2100}{21000} \right) \times 100 = 10%. \] Step 5: Conclusion The person incurred a loss of 10%.