Answer: a) 800
b)

Explanation:
The exponential growth function is represented by :-
, where A is initial value , b is the multiplicative rate of change and t is the time period.
Given : A bacteria culture starts with 100 bacteria and doubles in size every half hour.
i.e. A = 100 and b=2
Then, the exponential growth function to find the number of bacteris after t hours :_

At x=3

Hence, the there are 800 bacteria after 3 hours.