The key aspect of exponential growth:
In any time interval of a given length, the function value is multiplied by the same factor.
You invest money a at certain annual interest rate $p$. Interest is paid once a year. It is customary to use instead of the percentage the rate $r$ defined by $$r = \frac{p}{100}.$$

Every year you multiply your current capital by a factor (where your answer of course depends on $r$).
In $2$ years you multiply your initial capital with .
In $3$ years you multiply your initial capital with .
In $t$ years you multiply your initial capital with (where your answer depends on $r$ and $t$).
Supposing that your initial deposit is $I$, after $t$ years, your balance is
$f(t)$ = (where your answer depends on $r$, $t$, and $I$). (Remember that variables are case sensitive, you do need to use the proper upper or lower case for each variable.)