Chapter 3.3, Problem 18E

Tax Table Here are selected entries from the 2014 tax table that show the federal income tax owed by those married and filing jointly. The taxable income and the tax are both in dollars.

Taxable income	Tax
$\mathrm{72,\; 000}$	$9896$
$\mathrm{72,\; 200}$	$9926$
$\mathrm{72,\; 400}$	$9956$
$\mathrm{72,\; 600}$	$9986$
$\mathrm{72,\; 800}$	$\mathrm{10,\; 016}$
$\mathrm{73,\; 000}$	$\mathrm{10,\; 046}$
$\mathrm{73,\; 200}$	$\mathrm{10,\; 076}$
$\mathrm{73,\; 400}$	$\mathrm{10,\; 106}$
$\mathrm{73,\; 600}$	$\mathrm{10,\; 136}$
$\mathrm{73,\; 800}$	$\mathrm{10,\; 169}$
$\mathrm{74,\; 000}$	$\mathrm{10,\; 219}$
$\mathrm{74,\; 200}$	$\mathrm{10,\; 269}$

Over what two parts of this table is the tax a linear function of the taxable income? Find formulas for both linear functions, and explain in practical terms what the slopes mean.