hi I am in the middle of writing up my lab report for Preparation of a drug – The Synthesis and Structure of Aspirin. I have done all my caculations but I am stuck on the % yield.

I used 5g of Salicylic acid which has a RMM of 138

so (5/138)x100 = 3.623 moles

I used 7.5g of Ehtanoic Anhydride but I can't work out the RMM I am thinking that it is 102 is that right? And I know that Aspiring has a RMM of 180 but I'm stuck I don't know what to do next can some one give me any help so I can work it out please!