Two packed towers are designed for the same mass velocity of the gas. The first has liquid and gas flow rates of $30\:kg/s$ and $1.2\:kg/s$, respectively, while the corresponding flow rates in the second tower are $67.5\:kg/s$ and $1.8\:kg/s$. The ratio of the design diameter of the wider tower to that of the narrower tower is
- $2$
- $1.8$
- $1.5$
- $1.2225$