The chart has been completed in the picture attached.
Step-by-step explanation:
Step 1:
It is given that the number of bacteria doubles every 6 hours.
So if there are 1 million now, in 6 hours there would be double that i.e. 2 million and it will go on.
Step 2:
As the first column says the number of 6-hour periods, the second column is the actual number of hours.
So the second column is multiples of 6 so the second column is filled with;
0, 6, 12, 18, 24, 30, 36, 42 and 48.
Step 3:
The current population is calculated by multiplying the previous population by 2.
For 0 hours, the population = 3 million,
For 6 hours, the population = 
million,
For 12 hours, the population = 
million,
For 18 hours, the population = 
million,
For 24 hours, the population = 
million,
For 30 hours, the population = 
million,
For 36 hours, the population = 
million,
For 42 hours, the population = 
million, and
For 48 hours, the population = 
million.
So at the end of 48 hours, there will be approximately 768 million bacteria on the pinhead.
