Marginal profit = MR - MC
To maximize Gross Profit, MR must be at least equal to MC.
That means only the first 9 guests should be invited.
But Gross Profit must be net of Fixed Cost to see if there is any Net Profit
Fixed Cost = 100
Net Profit = Max Cumulative Gross Profit – Fixed Cost = 305 -100 = 205
Costs and opportunities, Profit maximization, Marginal optimization