Chemistry volumetric ysis?

a solution of an acid contains 7.3g of HOOC-(CH2)n-COOH per dm^3 of solution. 20.0cm^3 of this acid solution was titrated with NaOH solution, using phenolphthalein as indicator. in the titration, 25.00cm^3 of this alkali was used. the sodium hydroxide contained 1.36g of hydroxide ion per dm^3. what is the relative molecular m of the acid?