You're prepared to make monthly payments of $350, beginning at the end of this month, into an account that pays 10 percent interest compounded monthly. How many payments will you have made when your account balance reaches $40,000 ? Please show all calculations.

I got 7.53 using the Future Value of an annuity formula and solving for number of periods, I dont know how thats possible. help! And explain as thoroughly as you can please