A boiler was bought for P1,500,000 cost of installation and shipping amounted to P200,000. The estimated salvage value after 20 years is 10% of the unit cost. Twelve years later the boiler will be rehabilitated at a cost of P300,000. Salvage value and economic life were expected to increase by P50,000 and 5 years respectively. Using the sinking fund method with 10% interest, determine the book value at the end of 18 years.