If a computer costs $600.00 and the sales tax rate is 7.5 percent, what is the total cost of the computer?
$607.50
$615.00
$622.50
$645.00

The total cost of an article is its price before taxes plus taxes. Taxes are calculating by muliplying the price before taxes times the tax rate divided by 100. So, the tax of the computer is $600.00 * 7.5 /100 = $45.00. Then, the total cost of the computer is $600.00 + $45.00 = $645.00, which is the last option of the list.