Percentage/theoretical yield problem

Oct 2015
Suppose you prepare a sample of aspirin by heating 10g of salicylic acid with an excess of acetic anhydride. You obtain 6.2g of pure aspirin. What is the percentage yield of this reaction? Hint: first calculate the theoretical yield.

There are Lewis structure give of the reactants and products listing their molar mass as:
salicylic acid = 138g/mol
acetic anhydride = 102g/mol
aspirin = 180g/mol
acetic acid = 60g/mol

I know I need to start by writing a balanced equation...
C7H6O3 + C4H6O3 = aspirin (which I can't understand the molecular formula from the Lewis structure - but have googled as C9H8O4 - which is not going to help me in the exam!!!) + CH3CO2H

Now where do I go from here?