Answer
$f(t)=23.4*e^{-0.01t}$
Work Step by Step
We can convert the general function of:
$f(t)=A*b^{t}$ as: $f(t)=Q_0*(e^{-k})^{t}=Q_0*e^{-kt}$
In the exercise, we have:
$f(t)=23.4*0.991^{t}$
In order to get the desired form of the function we have to convert:
$0.991=e^{-k}$
We can use the logarithm for this:
$\log_e{0.991}=-k$
$\ln{0.991}=-0.009=-k$
Therefore the result will be:
$f(t)=23.4*e^{-0.009t}$