The formula for compound interest is:
\(I = P(1 + \frac{r}{n} ) ^{nt}\)
Where P is the amount you start with, r is the rate, t is the time, and n is the number of times the interest is calculated per year. So for you, this would look like:
\(I = 20000(1 + \frac{0.05}{1}) ^{1*7}\)
Hope it helps!
