The top 4 firms have (23 +22 +18 +12)% = 75% of the market.
The 4-firm concentration ratio is 0.75 or 75%.
To find surface area of 3D objects, you have to know the area formulas for basic shapes. For example, the area of a circle is

and the area of a rectangle is length times width. To find surface area of a cylinder, you will need to know both of those formulas, since the 3D shape involves both circles and rectangles.
Answer:
3= 1680
Step-by-step explanation: