Sorry if my picture sucks but I did it in paint and I'm not an artist.
Also I apologize if its hard to understand my work but its the way I did it.
Today I got to do question 7 in our homework book. You have to find the surface area of a rectangular prism with a hole in the middle, to solve it you need the formulas for the area of a rectangular prism and cylinder.
(Click on image to make it bigger)
Everything I did was normal math, I found the surface area for all the faces on the rectangular prism and for the cylinder. You need to find the area of the cylinder because you need to subtract the area of each circle on it from the total surface area, (if you want to read the explanation why, continue, if you already know why skip this and comment) because it's not part of the surface area, there's nothing there, no surface. Also you need the area of the cylinder to add to the total surface area because its part of the object's area. (If you were to paint the entire object you would have to paint the tunnel in the middle as well) Well that's pretty much it the picture should show my work.
If you didn't understand or if you found some mistakes please comment.