You would add up the percentages first, which would bring everything up to 35%. You would then take the original cost of the item, which is $30 and multiple it by the 35%.
The equation would look like...
30 x .35 =
This will give you $10.50, which isn't the final answer.
You would then subtract 10.50 from the $30 that was asked for at the beginning by the retailer.
Your final answer is $19.50. :) Which isn't a bad deal if I say so myself.