The final selling price is $256.50
Given:
Original Price = 400
1st discount = 25%
2nd discount = 10%
3rd discount = 5%
400 * 25/100 = 100 *1st discount value
400 - 100 = 300 *net of 1st discount
300 * 10/100 = 30 *2nd discount value
300 - 30 = 270 *net of 2nd discount
270 * 5/100 = 13.50 *3rd discount value
270 - 13.50 = 256.50 *net of 3rd discount, Final Selling Price.