Question 823731
John, eighteen years old, is three times as old as his brother. How old will John be when he is twice as old as his brother? 
18 = 3x 
6 = x
John is 18 years old
His brother is 6 years old
18 - 6 = 12
They are 12 years apart.
2 * 12 = 24
John will be 24 years old when he is twice his brother's age, 12 years old.