Agnes is 25 years old and her daughter, Jane is 6 years old. In how many years will Agnes be twice as old as Jane? Think carefully first, then make a decision:
Let the number of years after which Agnes will be twice as old as Jane be x. After x years, 25 + x = 2(6 + x). Solving the equation by expanding and collecting like terms gives: x - 2x = 12 - 25. Further solving gives: - x =  - 13. Multiplying both sides by - 1 gives x = 13. So, the answer is 13.