5 lamps of 60-watt burns for 10 hours. implies total KWh (units consumed) is
6 lamps of 100-watt burns for 10 hours. implies total KWh (units consumed) is
Total kWh consumed in a day = 6+3 = 9 KWh=9 units per day
For 30 days 270 units are consumed
1 rupee per unit, therefor for 270 units 270 rupees