Modules count from the Left to the right with the PROCESSOR considered number ZERO. Thus, the first carrier can hold 5 slots, the 2nd and 3rd, 6 each. (Power Units do not count)
Therefore, the one you are calling slot 7, should be the 2nd card in the 2nd carrier.
The 100-D, of what ever variety counts as 24 trunk ports, even if you only use 3 channels.
The trunk numbers for your slot 7 would depend on the number of line ports you have ahead of it.
So, if you had 3 408 cards (of what ever variety) ahead of your slot 7, (and some number of STATION cards) then the first trunk in that card would be trunk 13, or 813 using the default numbering of the system.