K - S = 28. (1) The sum of their ages now is 90 - 2*9 = 72. It gives you SECOND equation K + S = 72. (2) Add equations (1) and (2). You will get 2K = 28 + 72 = 100 ===============> K = 100/2 = 50. Hence, S = 72 - 50 = 22. ANSWER. K is 50 years old; S is 22 years old.