451: Growth Rate

Population of organism after n minutes is $P(n) = k*9^{(\frac{n}{2})}$.
What is the growth factor?

... algebraically stated, what is the ratio of P(t+1):P(t)?

Source:

#SATPrep Population of organism after n min is P(n)=k•9^(n/2) P( t+1):P(t)? #mathchat 

— David Marain (@dmarain) April 30, 2015