Find out the number of moles of sodium hydroxide utilized to dissolve the aspirin tablet. This will be the same in all three cases.
From your titration data, find out the number of moles of hydrochloric acid added as well as hence determine the number of moles of sodium hydroxide that did not react with the aspirin.
From the quantities determined so far, compute the number of moles of sodium hydroxide that reacted with the acetylsalicylic acid in the aspirin.
Remembering that 1 mole of acetylsalicylic acid reacts with 2 moles of sodium hydroxide, compute the number of moles of acetylsalicylic acid in the aspirin tablet.
Compute the mass of acetylsalicylic acid in the aspirin tablet.
Find out the percentage of acetylsalicylic acid in the aspirin tablet.