a son is 1/4 of his fathers age. the difference in their ages is 30. what is the fathers age. Declare variables: Let f be the father's age Let s be the son's age We're given two equations: s = f/4 f - s = 30. The reason why we subtract s from f is the father is older Using substitution, we substitute equaiton (1) into equation (2) for s: f - f/4 = 30 To remove the denominator/fraction, we multiply both sides of the equation by 4: 4f - 4f/4 = 30 *4 4f - f = 120 3f = 120 To solve for f, we divide each side of the equation by 3: 3f/3 = 120/3 Cancel the 3's on the left side and we get: f = 40