Correct option is (c) 20%
M.P. = Rs. 12, discount rate = 15%
∴ Net price after 1st discount = \(\frac{85}{100} \) x 12 = Rs. 10.20
Final selling price = Rs. 8.16
∴ Additional discount = Rs. 10.20 − Rs. 8.16 = Rs. 2.04
∴ Additional discount rate = \(\left(\frac{2.04}{10.20} \times 100\right)\)% = 20%.