For this case, what you should do is write an equation of the potential type to model the problem.
An equation of the potential type can be for example:
n (t) = A * (b ^ t)
Where
A: initial population
b: number of times the population grows
t: growth time (hours)
The equation that best describes this problem is
n (t) = 1 * (3 ^ t)
answer
n (t) = 1 * (3 ^ t)
