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
![f(4) = 530](https://img.qammunity.org/2021/formulas/mathematics/college/stpiulfmvde5935pyb6gxz73zpmirshkuh.png)
Explanation:
From the question we are told that
![f(t) = (6000)/(1 + Be^(-kt))](https://img.qammunity.org/2021/formulas/mathematics/college/h9vbt43dlfzdf48zdtuu2br73mlzm1sxe3.png)
Now at time t = 0 f(t) = 300 this because at the time the announcement was made the number of student present was
![f(0) = 300](https://img.qammunity.org/2021/formulas/mathematics/college/f1j7q7vt40didgjxm7c5mciyw540okqln8.png)
so
![f(0) = (6000)/(1 + Be^(-k(0)))](https://img.qammunity.org/2021/formulas/mathematics/college/co19mb6estel4p59qwar9pqheoy4hkoee0.png)
![300 = (6000)/(1 + Be^(-k(0)))](https://img.qammunity.org/2021/formulas/mathematics/college/qrfo83cgkh109de4atlpouw67maxn9alkt.png)
![1 + B = 20](https://img.qammunity.org/2021/formulas/mathematics/college/zdu5n9dl2wv1r4ur6iulwxageurgx0xb9h.png)
=>
![B = 19](https://img.qammunity.org/2021/formulas/mathematics/college/7z7emrg4znr92nkctplthcoo6tnuxz4xwm.png)
So the above equation becomes
![f(t) = (6000)/(1 + 19 e^(-kt))](https://img.qammunity.org/2021/formulas/mathematics/college/bpc2alhwpsndo6so125bpz298tkcp83mad.png)
Now at the given time t = 2hr
![f(2) = 400](https://img.qammunity.org/2021/formulas/mathematics/college/vx4acd8z0memcn68ypnjnmppjtclc6b1s7.png)
So
![f(2) = (6000)/(1+19e^(-2k))](https://img.qammunity.org/2021/formulas/mathematics/college/5cjuc28zv4pctgw9ba72nv0kg2yydpwvb2.png)
![1+ 19 e^(-2k) = 15](https://img.qammunity.org/2021/formulas/mathematics/college/r89b3zygo1f1be5cvkryejb6byiqtp2o6h.png)
![19 e^(-2k) = 14](https://img.qammunity.org/2021/formulas/mathematics/college/thpmr71s0bho2p5ob6s1zxqy1q5cl2bxq8.png)
![e^(-2k) = 0.7368](https://img.qammunity.org/2021/formulas/mathematics/college/uq767nqs341yra6qpetnayswixj8bf47c8.png)
![-2k =-0.3054](https://img.qammunity.org/2021/formulas/mathematics/college/vzi15q4maj9ml508k1h01y4u1gjzww3k9s.png)
So the equation is now
![f(t) = (6000)/(1+ 19e^(-0.1527t))](https://img.qammunity.org/2021/formulas/mathematics/college/83p16okt0ojiav8mqee1qa0i9rtv91tivq.png)
Now at t = 4 hrs we have that
![f(4) = (6000)/(1+ 19e^(-0.1527* 4))](https://img.qammunity.org/2021/formulas/mathematics/college/kvfhatxp7fck8nxwix8pi3h4eh2lln9idt.png)
![f(4) = 530](https://img.qammunity.org/2021/formulas/mathematics/college/stpiulfmvde5935pyb6gxz73zpmirshkuh.png)