If CH3 + CO -> CH3COOH, then CH3 and CH3COOH react and form in a 1:1 ratio. Thus:
mol(CH3) x .88 = mol(CH3COOH)
This expression says that 88% of the methanol reacted is used to produce acetic acid. To find the moles of CH3 needed, you need to work backwards since you are given the mass of product. So, given the mass of CH3COOH, find the moles of CH3COOH using its molar mass, plug it into the expression and then solve for moles of CH3.