In aggregate, by what percentage did the Bicycle Bell backers pledge more than the minimum at each level? That is, if the pledge level was $15 and backers pledged $18, they would be pledging 20% more than the minimum at that level. You don't have the individual pledges, but you have the total pledged (in the Pledged column) as well as the number of backers at each level. You can calculate the aggregate percentage above the minimum from that data