The population of a city in $\displaystyle {1906}$ was $\displaystyle {15},{311}$, and it doubles every $\displaystyle {6}$ years. What will the population be in:

(a) in $\displaystyle {1942}$?

(b) in $\displaystyle {1918}$?

(c) in $\displaystyle {1960}$?