50 bacteria land on your tooth and they quadruple in number every hour, what is the equation?

50 bacteria land on your tooth and they quadruple in number every hour, what is the equation?

$\begin{array}{|l|lcl|} \hline \text{now} & 50 \ \text{ bacteria} &=& 50 \cdot 4^0 \ \text{ bacteria}\\ \text{after } 1 \text{ hour} & 50\cdot 4 \ \text{ bacteria} &=& 50 \cdot 4^1 \ \text{ bacteria}\\ \text{after } 2 \text{ hours} & (50\cdot 4^1)\cdot 4 \ \text{ bacteria} &=& 50 \cdot 4^2 \ \text{ bacteria}\\ \text{after } 3 \text{ hours} & (50\cdot 4^2)\cdot 4 \ \text{ bacteria} &=& 50 \cdot 4^3 \ \text{ bacteria}\\ \text{after } 4 \text{ hours} & (50\cdot 4^3)\cdot 4 \ \text{ bacteria} &=& 50 \cdot 4^4 \ \text{ bacteria}\\ \text{after } 5 \text{ hours} & (50\cdot 4^4)\cdot 4 \ \text{ bacteria} &=& 50 \cdot 4^5 \ \text{ bacteria}\\ \cdots & \cdots&&\cdots\\ \text{after } n \text{ hours} & &=& 50 \cdot 4^n \ \text{ bacteria}\\ \hline \end{array}$