Let the total work be \( L \) (in hours).
\[ \frac{L}{72} + \frac{L}{64} \]
Finding the LCM of 72 and 64, which is 4608:
\[ \frac{64L + 72L}{4608} = \frac{136L}{4608} \]
Work done per hour:
\[ \frac{L}{33.88} \]
\[ \frac{L}{64} \div \frac{L}{33.88} \times 100 \]
Substituting values:
\[ \frac{136L}{4608} \times 100 \]
\[ = 53\% \]
Thus, the correct answer is 53% (Option B).
An electricity utility company charges ₹7 per kWh. If a 40-watt desk light is left on for 10 hours each night for 180 days, what would be the cost of energy consumption? If the desk light is on for 2 more hours each night for the 180 days, what would be the percentage-increase in the cost of energy consumption?