To determine the number of bacteria at 8:00 a.m., we need to consider that the bacteria double every hour.
Since we know that at 9:00 a.m. there are 120 bacteria, we can find the number of bacteria at 8:00 a.m. by halving the count at 9:00 a.m. because bacteria doubled from 8:00 a.m. to 9:00 a.m.
Let \( n \) be the number of bacteria at 8:00 a.m. Therefore, the relationship can be represented as:
\[ 2n = 120 \]
To find \( n \):
\[ n = \frac{120}{2} = 60 \]
So, at 8:00 a.m., there were 60 bacteria. Thus, the correct response is:
2n = 120; at 8:00 a.m., there were 60 bacteria.