An old bulb of 75 W and an LED bulb of 11 W give about the same light.

Step 1. (a) Old bulb. $0.075\ \text{kW} \times 6\ \text{h} \times 30 = 13.5\ \text{kWh}$.

Step 2. (a) LED. $0.011\ \text{kW} \times 6\ \text{h} \times 30 = 1.98\ \text{kWh}$.

Step 3. (b) $13.5\ \text{kWh} - 1.98\ \text{kWh} = 11.52\ \text{kWh}$.

Step 4. (c) $11.52 \times$ ₹$7 =$ ₹$80.64$.