HELP with chemistry please

Give the following equation:
C7H6O3 + C4H6O3 --> C9H8O4 + HC2H3O2

What mass of acetic anhydride (C4H6O3) is needed to completely consume 1.00 x 10^2 g of salicylic acid (C7H6O3)?

Please explain this to me!

Note: All calculations of molar masses are to be calculated to one decimal place.

the stoichiometry of the reagents (the ratio of acetic anhydride needed to salicylic acid) is 1:1 so you need the same number of molecules of acetic anhydride as salicylic acid. the number of molecules used in reactions is huge so numbers of molecules are measured in moles. the number of moles of salicylic acid used is n=M/Mr that is number of moles= mass of substance/mass per mole. Mass per mole is worked out by adding together the mass of each atom in the molecule, i.e. CH4 would be 12(C) + 4xH(1) =16. once you know how many moles of salicylic acid you are using, the number of moles of acetic anhydride will be the same, so rearrange n=M/Mr to M=n x Mr remembering to use the mass per mole (Relative molecular mass) of acetic anhydride and you have your answer! hope this helps.