Acetic acid (CH3COOH) reacts with isopentyl alcohol (C5H12O) to yield the ester isopentyl acetate which has the odour of bananas. If the yield from the reaction is 45%, how many grams of isopentyl acetate are formed when 3.90 g of acetic acid and 6.28 grams of isopentyl alcohol are reacted?

Question

So i found the limiting reagent,Drbob222 said "use that reagent and the number of grams, convert to moles, then convert to moles of the product. That will be the theoretical yield, in moles"
how do i convert the reagent and the number of grams into moles?

thanks