15- holder, are only included in taxable income in proportion to the time that the assets have been held by the taxpayer, as follows: When the Time Elapsed Between Acquisition and Sale, The Percentage of Merger or Liquidation is: Taxable Gain is: Up to 2 years 100% From 2 to 4 years 80% From 4 to 6 years 60% From 6 to 8 years 40% From 8 to 10 years 2 0% Over 10 years Not taxable The gain will not be taxable, regardless of the lapse of time between acquisition and sale of the fixed assets if, within the year following the sale the taxpayer applies the proceeds to the acquisition of other fixed assets for industrial, agricultural, livestock raising or fishing purposes, with the previous authorization of the Treasury Department and "based on general rules issued for the purpose". It should be noted that this authorization is not granted to commercial enterprises. 19. Installment sales: For installment sales on which payment of at least 50% of the agreed-upon price is deferred, the taxpayer has the option of including the total profit in the year in which the sale is made or proportionate-ly in the years in which collection of the installments is actually made. This option was not clear in the previous law. This option is now available not only for installment sales of inventories but for fixed assets as well; in the case of fixed assets, if the installment sale treatment is adopted, only the applicable percentage of profit, in accordance with the table in preceeding point 18, is taxable each year. The method elected cannot be changed without the prior au-thorization of the Treasury Department. 20. Depreciation and _amortization: As in the previous law, the new law only stipulates as a general provision the straight-line method of depreciation and amortiza-tion, at fixed annual rates which are applicable to the original cost of the investment. The taxpayer can elect to use rates up to the limits set forth below, which can only be modified in special cases with prior authorization by the Treasury Department: a) 5% for amortization of intangible fixed assets and deferred charges.