Line DQ is equal to 7. Since point Q is the centeriod, this means that line DQ will equal the same as line QD. Thus, line QD is 7 making like DQ 7 as well. Hope that helped :))
You take ten percent of 33, which is 3.3, and subtract it from the original price.
33-3.3=29.7 which means the final price is $29.70
