(1) From the condition, Sam + Tony = 36 Sam - Tony = 4 Add the equations. You will get 2*Sam = 40, Sam = 20. Hence, Tony is 16 years old. (2) Three years ago, the sum of ages Mark + Tony was 33 years. Hence, currently it is 33+3+3 = 39 years: Mark + Tony = 39, or Mark + 16 = 39. Hence, Mark = 39-16 = 23. ANSWER. Mark is 23 years old; Tony is 16 years old; Sam is 20 years old.