Instruction: Mary is twice as old as Elizabeth. John is two years older than Elizabeth. John's and Elizabeth's ages combined equal eight. How old is Mary? Explain your reasoning.

Response: Let's call Elizabeth's age x. We know that John is two years older than Elizabeth, and their combined ages are 8. So x + x + 2 = 8, meaning Elizabeth is 3. Mary is twice Elizabeth's age, which makes Mary 6.