Let's begin by calling Sarah's age now as X. As Ralph is 3 times as old as Sarah, X times 3 = 3X. Hence, Ralph's age is 3X. In six years, Ralph will be twice as old as Sarah. To calculate six years from now, add 6 to X for Sarah, and 6 to 3X for Ralph. As Ralph is twice as old as Sarah and we want to find the difference between the ages to calculate X, multiply X+6 by 2. You'll get 2X+12. Therefore, 2X+12=3X+6. Deduct 6 from 3X+6 as we want to isolate the variable. Because you did that to one side, you have to deduct 6 from 2X+12. Hence, now you have 2X+6=3X. X=6. Ralph's age is 3X, so 6 times 3 is 18. Ralph is 18 years old.
