How do I calculate gross margin (%) for this problem?

3 Number of Additional Visits per day 0 4 1350 45 40.64 54,864 5 Total monthly visits 6 Total daily visits 7 Net revenue per visit 8 Total net monthly revenue 9 10 Total current costs 11 Total incremental costs 12 Current & Incremental Costs 13 14 Monthly profit (loss) 15 Gross margin (%) 58,061 0 58,061 -3,197 1.6