if the cost price of 15 mobile phones is equal to selling price of 18 chargers and cost price of 15 earphones is equal to the selling price of 21 chargers. If the cost price of the earphones is Rs. 1491 then find the cost price of the charger if it is sold at a loss of 25%? (in rupees)

Let CP_m = cost price of mobile, CP_e = cost price of earphone, CP_c = cost price of charger, SP_c = selling price of charger. Given: 15 × CP_m = 18 × SP_c, 15 × CP_e = 21 × SP_c, CP_e = 1491, and charger sold at 25% loss means SP_c = 0.75 × CP_c. From the second equation: SP_c = (15 × 1491)/21 = 1065. Then CP_c = SP_c / 0.75 = 1065/0.75 = 1420. Option B is correct.