Assume 1 g of the 3 g is aspirin. Show by

calculation that 7 mL of 6 M HCl is enough
to completely neutralize the conjugate base
of aspirin to the neutral compound.

mols conjugate base = grams/molar mass = ?

1 mol conjugate base aspirin = 1 mol HCl.
M HCl = mols HCl/L HCl
You know M and you know L HCl, solve for mols and compare mols HCl with mols conjugate base.