Let x be the Joseph's age. Then the father's age is 7x years. One age ago 7x-1 = 9*(x-1) Simplify and solve 7x - 1 = 9x - 9 9 - 1 = 9x - 7x 8 = 2x. x = 8/2 = 4. ANSWER. 4 years and 28 years.