Since the bacteria double every hour, we can denote the number of bacteria at 8:00 a.m. as \( n \). Given that at 9:00 a.m. there are 120 bacteria, we can express this relationship as:
\[ 2n = 120 \]
To find \( n \) (the number of bacteria at 8:00 a.m.), we can solve the equation:
\[ n = \frac{120}{2} = 60 \]
Therefore, the equation that represents the number of bacteria at 8:00 a.m. is \( 2n = 120 \), and the number of bacteria at that time was 60.
So the correct response is:
2n = 120; at 8:00 a.m., there were 60 bacteria.