Let x be that additional discount, expressed as a decimal. Then you have this equation (1-0.25)*(1-0.15)*(1-x) = 1 - 0.45 or 0.75*0.85*(1-x) = 0.55 1 - x == 0.862745. Hence, the additional chain discount should be 1 - 0.862745 = 0.137255 = 13.7255% ANSWER