Step 1: Understand the nature of growth.
Since the rate of growth of bacteria is proportional to the amount present, the growth follows the law of exponential growth.
Step 2: Use the given information.
It is given that the number of bacteria doubles in 3 hours. This means:
\[
N(3) = 2N_0
\]
Step 3: Find growth in 6 hours.
Since 6 hours is twice 3 hours, the bacteria will double again in the next 3 hours. Hence:
\[
N(6) = 2 \times 2N_0 = 4N_0
\]
Step 4: Final conclusion.
The number of bacteria after 6 hours becomes four times the original number.