The total energy consumed by the refrigerator in 30 days =400 x 8 x 30 = 96000 Wh = 96 kWh The total energy consumed by the iron box in 30 days =750 x 2 x 30 = 45000 Wh = 45 kWh The total energy consumed by the refrigerator and iron box is = 96 kWh + 45 kWh = 141 kWh The sum of bill amount for 141 kWh at rate of Rs. 3 per 1 kWh is =141 x 3 = Rs. 423