Answer: 39 minutes 51 seconds
Explanation:
Nt=N0 * 2^n
N0=Initial population
n=number of times bacteria divide
700=320*2^n
log2(700/320)=1.129283017=n
45/1.129283017=39.84829252 minutes
0.84829252*60=50.89755135≈51seconds
so the answer is
39minutes and 51seconds