Here are the calculations for computing the margin.
Price of the Coffee Cup= $2.10
Cost on the Coffe Cup= $0.30
Net Profit = $2.10 - $ 0.30 = $1.8
Now to Calculate the Margin we need to do the following calculation:
Profit/Price of the Coffee Cup= ($1.8 / $2.10) * 100= 85% Approximately.