y = 7
I have attached the step explanation in the photo
Answer:
Radius =6.518 feet
Height = 26.074 feet
Step-by-step explanation:
The Volume of the Solid formed = Volume of the two Hemisphere + Volume of the Cylinder
Volume of a Hemisphere 
Volume of a Cylinder 
Therefore:
The Volume of the Solid formed

Area of the Hemisphere =
Curved Surface Area of the Cylinder =
Total Surface Area=

Cost of the Hemispherical Ends = 2 X Cost of the surface area of the sides.
Therefore total Cost, C

Recall: 
Therefore:

The minimum cost occurs at the point where the derivative equals zero.


![-27840+32\pi r^3=0\\27840=32\pi r^3\\r^3=27840 \div 32\pi=276.9296\\r=\sqrt[3]{276.9296} =6.518](https://tex.z-dn.net/?f=-27840%2B32%5Cpi%20r%5E3%3D0%5C%5C27840%3D32%5Cpi%20r%5E3%5C%5Cr%5E3%3D27840%20%5Cdiv%2032%5Cpi%3D276.9296%5C%5Cr%3D%5Csqrt%5B3%5D%7B276.9296%7D%20%3D6.518)
Recall:

Therefore, the dimensions that will minimize the cost are:
Radius =6.518 feet
Height = 26.074 feet