No, there's definitely enough information to solve this problem. What you've done so far is great, but you've for some reason stopped five feet short of the metaphorical goal tape. So let's keep going and finish up. You've correctly identified that the interest rate must be 10% (0.1). Suppose the principal is $1. We know that the balance is $2 after ten years. How much interest, in dollars, does the account accrue each year? What will the account balance be after eleven years? After twelve years? Are you seeing a pattern? When do you suppose the account balance will be $3 (that is, triple the original amount)?
Now suppose the principal is $2. How much interest, in dollars, does the account accrue each year? When will the account balance be $6? How does this answer compare to the answer when the principal was $1? Does that result make sense to you? What does it tell you? Finally, suppose the principal is some unknown value P. How much interest, in terms of P, does the account accrue each year? What expression represents triple the original amount? When will the account balance be this value?
