Complete Question
The complete question is shown on the first uploaded image
Answer:
The number of student that have heard the announcement after 4 hours is

Explanation:
From the question we are told that

Now at time t = 0 f(t) = 300 this because at the time the announcement was made the number of student present was

so



=>

So the above equation becomes

Now at the given time t = 2hr

So





So the equation is now

Now at t = 4 hrs we have that

