n m = -18 or -36 or -108 then k = 7 or 3 or 7 ..but now K is not a multiple of 9 ??so how can D always be true ??Please note question does not mention that n is a positive integer or M is a positive integer .if n is a negative integer as shown above then m will be negative and the sum of the digits of M will not always be 9 so please do explain how D is always true ??The sum of the digits of -18 i