Answer:
For this case we know from the initial conditions that the value for a = 123 since is the starting value, so our model is given by:

Now we can use the other condition given "the number of people who had watched it was increasing by 30% every 3 hours", so for example after the first t =3 hours we will have a value for y = 1.3*123= 159.9, and using this condition we have this:

We can divide both sides by 123 and we got:

Now we can apply natural log on both sides and we have:


And our model for this case would be:

Explanation:
For this case we want to construct and exponential model given by this general expression:

Where a is the initial amount and b the growth/decay constant.
For this case we know from the initial conditions that the value for a = 123 since is the starting value, so our model is given by:

Now we can use the other condition given "the number of people who had watched it was increasing by 30% every 3 hours", so for example after the first t =3 hours we will have a value for y = 1.3*123= 159.9, and using this condition we have this:

We can divide both sides by 123 and we got:

Now we can apply natural log on both sides and we have:


And our model for this case would be:
