Use figure 4.14 of CAP 696 (get this in front of you, preferably with an example question). First work out the all-up mass, using the left-hand side of the form if necessary, but effectively just adding everything that the aircraft has on board at the time to the aircraft itself, often in practice by adding fuel and traffic load to DOM. Then enter the table on the right-hand side of the form, entering at the top with the DOI as given in the question.
Follow down onto the next line, which is for the forward baggage hold, and labelled "1" at the left. For each 1000 kg in this hold move left as shown by the arrow; this means that each block is 1000 kg, and each small mark is for 100 kg. Move from this point straight down to the next line, labelled "4" and repeat the exercise for the aft baggage compartment, except now the arrow points the other way, and therefore change index to the right.
The next 7 lines are for different areas of the passenger compartment, 0a to 0g. Move straight down each time to the line, then follow the arrow either left or right, each time a full block represents 10 people in that section of the cabin, the index change getting smaller of course towards the centre of the cabin, near to the aircraft's C of G. The centre-most section has no significant effect.
After 0g there is a line for the Fuel index. The fuel index can be found from Figure 4.13. The line is used in the same manner, each small mark representing a fuel index of 1.
From this point follow straight down to intersect with a horizontal line at the aircraft mass, the intersection giving the aircraft C of G as % MAC.
Hope this helps.
Send Clowns
Flight Planning instructor (and sometime flingwing driver, although flying planks at the moment)
BCFT