Let x be the son’s age, and y be the father’s age. Then we have: • y = x + 30 (the father is 30 years older than the son) • y + 10 = 3(x + 10) (in 10 years, the father will be three times as old as the son) To solve for x and y, I substituted the first equation into the second one, and got: • (x + 30) + 10 = 3(x + 10) • Simplifying and rearranging, I got: • x = 10 Then I plugged x = 10 into the first equation, and got: • y = 10 + 30 • y = 40 So the son is 10 years old, and the father is 40 years old.