Salina current has an account balance of $1,047.69. her initial deposit on the account was $630 and it earned 3.9% simple interest. how long has she held the account?

All you have to do is take $630 and multiply it by 3.9% to get $24.57.  Then take $1,047.69 and subtract the initial amount in the account ($630) to get $417.69 then divide that by the interest per month I assume ($24.57) to get 17.  So I believe that the account has been held for 17 months.  To check simply take $630 multiply it by 3.9% then multiply that by 17.  I hope this helped if not please tell me where I went wrong.
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The answer is 225 miles per 4.5 hours. hope this ; )