An investor spent 2.5 millions BD to build a hydroelectric power plant that consists of 20 identical turbine-generator units with an overall plant efficiency of 90%. The gross head of the dam is 150 m and the flow rate through each turbine is 55 Liter/sec. The plant operates 78.36% of time throughout the year and the electricity generated is sold to the utility company at a rate of 0.100 BD/kWh. Q. In how many years will the investor be paid