The sales tax in san francisco is 8.5%, while in oakland it is 8.75%. what is the price difference in buying a $21,000 (before tax) car in oakland and san francisco?

San Francisco : 
Sales Tax = 8.5% x $21000 = 0.085 x 21000 = 1786
Price = $21000 + $1786 = $22785

Oakland:
Sales Tax = 8.75% x $21000 = 0.075 x 21000 = 1837.50
Price = $21000 + $1837.50 = $22837.50

Difference in price = $22837.50 - $22785 = $52.50

$52.50

OR  

8.75% - 8.5% = 0.25%

Difference in price = 0.25% x 21000 = 0.0025 x 21000 = $52.50