The molarity of the acetic acid solution is calculated as below
calculate the moles of KOH used
moles =molarity x volume
= 20.9 x0.267 = 5.58 moles
write the reaction equation
KOH + CH3COOH = CH3COOK + H2O
since the reacting ratio between KOH to CH3COOH is 1:1 the moles of CH3COOH is also = 5.58 moles
molarity of CH3COOH = moles/volume
=5.58 /29.1 =0.192 M