The only questions that ask you to do this are based on the MRJT1 Load/Trim sheet.
For example (I just made this one up):
If DOM is 45000, and C of g is at 20% MAC what is the DOI.
Go into the Load/Trim sheet and find 45000 Kg on the left side of the lower scale.
Move horizontally right to the 20% MAC line.
Drop vertically down to the bottom of the graph and read off about 54.