An electric bulb marked with 100 V-60 W is used for 5 h in a week. What is the cost of electricity, if the rate is ₹ 6 per unit?
Given, power, P 
Time, t = 5 × 7 = 35h
Rate of electricity = ₹ 3 per unit
∴ The energy consumed in a week = Pt = 
The cost of electricity at the rate of = ₹ 3 per unit is = 3 × 2.1 = ₹ 6.3