I would have to say A - Mean; because the data is skewed and there are outliers.
This is because the median of this would not be accurate for the number of kids that read no books and the random three kids that read ten. Mean, however, would find the true median within the plot and utilize and take into account the outliers and how skewed the data is.
You would turn 15% into a decimal. Which would be .15, and then do .15 times $29.99 which is $29.84. Then you would subtract the $29.99 minus the $29.84