Question

1 - 500 principal earning 4% compounded quarterly, after 6 year.

Answer 1

You'll have $634.87 after 6 years at 4% compounded quarterly, thus B:
You'll have $3,619.80 after 6 months at 6.75% compounded monthly, thus A:

Formulas where n = 1 (compounded once per period or unit t)
1.  Calculate Accrued Amount (Principal + Interest) A = P(1 + r)^t
2. Calculate Principal Amount, solve for P.  P = A / (1 + r)^t
4. Calculate the rate of interest in decimal, solve for r. r = (A/P)1/(^t - 1)
5. Calculate rate of interest in percent. ...Calculate time, solve for t.