Answer:
![9\pi \text{ cubic meters per hour}](https://tex.z-dn.net/?f=9%5Cpi%20%5Ctext%7B%20cubic%20meters%20per%20hour%7D)
Step-by-step explanation:
Since, the surface area of a cylinder,
................(1)
Where,
r = radius,
h = height,
If ![A= 36\pi\text{ square meters}, h = 3\text{ meters}](https://tex.z-dn.net/?f=A%3D%2036%5Cpi%5Ctext%7B%20square%20meters%7D%2C%20h%20%3D%203%5Ctext%7B%20meters%7D)
![36\pi = 2\pi r^2 + 2\pi r(3)](https://tex.z-dn.net/?f=36%5Cpi%20%3D%202%5Cpi%20r%5E2%20%2B%202%5Cpi%20r%283%29)
![18 = r^2 + 3r](https://tex.z-dn.net/?f=18%20%3D%20r%5E2%20%2B%203r)
![\implies r^2 + 3r - 18=0](https://tex.z-dn.net/?f=%5Cimplies%20r%5E2%20%2B%203r%20-%2018%3D0)
( by middle term splitting )
![r(r+6)-3(r+6)=0](https://tex.z-dn.net/?f=r%28r%2B6%29-3%28r%2B6%29%3D0)
![(r-3)(r+6)=0](https://tex.z-dn.net/?f=%28r-3%29%28r%2B6%29%3D0)
By zero product property,
r = 3 or r = - 6 ( not possible )
Thus, radius, r = 3 meters,
Now, differentiating equation (1) with respect to t ( time ),
![\frac{dA}{dt}= 4\pi r\frac{dr}{dt} +2\pi(r\frac{dh}{dt} + h\frac{dr}{dt})](https://tex.z-dn.net/?f=%5Cfrac%7BdA%7D%7Bdt%7D%3D%204%5Cpi%20r%5Cfrac%7Bdr%7D%7Bdt%7D%20%2B2%5Cpi%28r%5Cfrac%7Bdh%7D%7Bdt%7D%20%2B%20h%5Cfrac%7Bdr%7D%7Bdt%7D%29)
∵ h = constant, ⇒ dh/dt = 0,
![\frac{dA}{dt} = 4\pi r \frac{dr}{dt} +2\pi h \frac{dr}{dt}](https://tex.z-dn.net/?f=%5Cfrac%7BdA%7D%7Bdt%7D%20%3D%204%5Cpi%20r%20%5Cfrac%7Bdr%7D%7Bdt%7D%20%2B2%5Cpi%20h%20%5Cfrac%7Bdr%7D%7Bdt%7D)
We have,
![9\pi = 4\pi (3) \frac{dr}{dt}+2\pi (3)\frac{dr}{dt}](https://tex.z-dn.net/?f=9%5Cpi%20%3D%204%5Cpi%20%283%29%20%5Cfrac%7Bdr%7D%7Bdt%7D%2B2%5Cpi%20%283%29%5Cfrac%7Bdr%7D%7Bdt%7D)
![9\pi = (12\pi + 6\pi )\frac{dr}{dt}](https://tex.z-dn.net/?f=9%5Cpi%20%3D%20%2812%5Cpi%20%2B%206%5Cpi%20%29%5Cfrac%7Bdr%7D%7Bdt%7D)
![9\pi = 18\pi \frac{dr}{dt}](https://tex.z-dn.net/?f=9%5Cpi%20%3D%2018%5Cpi%20%5Cfrac%7Bdr%7D%7Bdt%7D)
![\implies \frac{dr}{dt} =\frac{1}{2}\text{ meter per hour}](https://tex.z-dn.net/?f=%5Cimplies%20%5Cfrac%7Bdr%7D%7Bdt%7D%20%3D%5Cfrac%7B1%7D%7B2%7D%5Ctext%7B%20meter%20per%20hour%7D)
Now,
Volume of a cylinder,
![V=\pi r^2 h](https://tex.z-dn.net/?f=V%3D%5Cpi%20r%5E2%20h)
Differentiating w. r. t. t,
![\frac{dV}{dt}=\pi ( r^2 \frac{dh}{dt}+h(2r)\frac{dr}{dt})=\pi ((3)(6) (\frac{1}{2})) = 9\pi \text{ cubic meters per hour}](https://tex.z-dn.net/?f=%5Cfrac%7BdV%7D%7Bdt%7D%3D%5Cpi%20%28%20r%5E2%20%5Cfrac%7Bdh%7D%7Bdt%7D%2Bh%282r%29%5Cfrac%7Bdr%7D%7Bdt%7D%29%3D%5Cpi%20%28%283%29%286%29%20%28%5Cfrac%7B1%7D%7B2%7D%29%29%20%3D%209%5Cpi%20%5Ctext%7B%20cubic%20meters%20per%20hour%7D)