Answer:
B) The initial number of subscribers.
Explanation:
The given equation is:


We can compare this equation with the general model of exponential growth/decay:

Here A represents the initial amount, r represents the rate of decay and t represents the time in years.
Comparing both equations, we can see that 42,000 represents the Initial Quantity which in this case is the initial number of subscribers.
So option B gives us the correct answer.