saving up some money and depositing $350 every month into account with 3.5% interest rate compounded monthly.

a) How much money should I have saved up after 5 years?

b) When I checked, my account had $22,537.80. Thinking back, I realized that I did forget one payment but can't remember exactly when it was. Which payment I forgot to deposit?

I got 22,913.14 for part a. I do not know how to do part b. I am doing all calculations by hand.