I finally picked up 4 sheets of 4'x8' MDF for this project, I picked up an extra sheet in case I messed up. I started drawing out cabinet side 1 according to the book dimensions and boy am I confused.

I measured the real dimensions of the MDF and they are 49"x97"

According to the book dimensions cabinet side 1's back side length is 74" long, the way I read it is it's 74" long until it angles towards the very top of the cabinet.

The monitor shelf that is cut from the same piece of MDF is 22"x26" so according to my math 22+74=96 BUT according to the dimensions in the book, between the monitor shelf and the back side angle there is 16 squares or 16 inches in between, that's impossible if the back side is 74" long since 74" + 16" = 90" that plus the 22" for the monitor shelf puts me at 112"

What am I not understanding??!?!? This is probably something super simple but I've never worked with wood or anything like this before this project so go easy.

I'm talking about the area where the red line is, hope that makes it more clear. I guess I don't know at what measurement the angle starts...