The purchase price of a camera is $84 the king cases 12% the purchase price tax is 6% subtotal what is the total cost for the camera and case plus tax

(Are you saying the king case is an additional 12% of $84? I think you should word the question a bit more clearly). 

12% = 12/100 = 0.12 multiplied by $84 = $10.08 = $84 + $10.08 = $94.08

We have $94.08 so far (king case and camera price combined). 

Tax is 6%, so 6/100 = 0.06 multiplied by $94.08 = $5.64
Add $5.64 to the $94.08 total we calculated.

$94.08 + $5.64 = $99.72 <=== this is our total cost plus tax.