Sam bought brushes for $8, a palette for $5, and oil paints for $15. he paid $29.82 in all. what sales-tax rate did sam pay?

Total purchased w/o tax: $8 +$5 + $15 = $28
He paid (w/tax) $29.82 so 
$ 29.82 - $28 = $1.82 (sale tax)

Now we need to find the sales tax rate:

$1.82 / $28 * 100 = 0.065 *100% = 6.5%

Double check:

$28 *6.5 / 100  = $1.82

$28 + $ 1.82 =  $29.82 total amount he paid..

So the sales tax rate is 6.5%

Ais the answer to your ques