HELP ME WITH FORMULAS PLEASE?

Hi all,

I need a set of 3 to 4 formulas which would show a monthly grow of accrued interest on each of the new amounts eg:

formula 1:Month 1- 15000 x 0.034 = 510
15000 + 510 = 15510

Month 2 - 15510 x 0.034 = 527.34
15510 + 527.34 = 16037.34

Formula 2:Month 1 - 15000 x 0.034 = 510
15000 + (510 - 300) = 15210

Month 2 - 15210 x 0.034 = 517.14
15210 + (517.14 - 300) = 15427.14

Formula 3&4: This is difficult for me to show on numbers but I need to calculate according to the previous examples what the outcome would be after eg. 5 years(54 months) or ten years etc. as you can't just take one amount and multiply it.

So each month the main value increases but the interest stays the same and the interest is caculated on each increased main value.

CAN SOMEONE PLEASE HELP ME WITH THIS???