Special tax; computation.
In lieu of the income and franchise tax rates prescribed in s. 71.27, there shall be assessed, levied and collected upon the taxable income of every corporation whose principal source (defined for purposes of this subchapter as being 50 percent or more) of gross income is the urban mass transportation of passengers a special income tax of 50 percent determined in accordance with this chapter, except that:
(a)#
United States income, excess or war profits and defense taxes shall be allowed as a deduction from gross income to the extent of the total payment actually made during the tax year.
(b)#
A deduction shall be allowed from such taxable income before the imposition of the special tax levied by this section, in an amount equivalent to 8 percent of the amount by which the cost of the property of such corporation used and useful in providing its urban mass transportation of passengers exceeds the cumulated amount of the depreciation accrued against such property as of the end of the fiscal year for which the income or franchise tax return is filed.
(c)#
An amount shall be added to such taxable income, before imposition of the special tax levied by this section, which amount shall be equivalent to the interest paid during the year in the operation of the business from which its income is derived.