Time period for compound interest

For half-yearly compounding, interest rate $r = \frac{4}{2} = 2\%$.

$A = P\left(1 + \frac{r}{100}\right)^n$ $6632.55 = 6250 (1.02)^n$ $1.061208 = (1.02)^n$

Since $1.02^3 = 1.061208$, $n = 3$ half-years = $1.5 = \frac{3}{2}$ years.