if the population quadruples every period say hour, that means the "rate of growth" is 300%, so whatever the current amount, increased by 3 times as much is 4 times the current amount, or a quadrupled amount.
[tex]\bf \qquad \textit{Amount for Exponential Growth}\\\\
A=I(1 + r)^t\qquad
\begin{cases}
A=\textit{accumulated amount}\\
I=\textit{initial amount}\to &74\\
r=rate\to 300\%\to \frac{300}{100}\to &3.00\\
t=\textit{elapsed time}\\
\end{cases}
\\\\\\
A=74(1+3)^t\implies A=74(4)^t[/tex]
