124. Marriage penalty eliminated. The value of the expression

Question

4220 + 0.25(x 30,650)
is the 2006 federal income tax for a single taxpayer with
taxable income of x dollars, where x is over $30,650 but
not over $74,200.
a) Simplify the expression.
b) Find the amount of tax for a single taxpayer with
taxable income of $40,000.
c) Who pays more, a married couple with a joint taxable
income of $80,000 or two single taxpayers with
taxable incomes of $40,000 each? See Exercise 123.