How would you make a serial dilution if you have a starting value 100mM of X

Question

The are the values of X show different dilutions.
Volume variables (x) mL
0
1
3
1
10
30
100

We starting out with 100mM of X which would be considered its concentration. In order to describe how to do a serial dilution I need to figure out the dilution factor from the volume variables. She wants us to describe how when starting from 100mM of concentration we can obtain those volumes.

Df1= 100ml/30mL = 3.333
Df2= 30mL/ 10= 3
Df3= 10mL/3= 3.333
Df4= 3/1 = 3
Df5= 3/1= 3
so I guess she wants us to work our way from the bottom up so I obtained a dilution factor of 3.333 and 3.

to find out the concentration I have the formula

C= C1/Dfactor
C= 100mM/ 3.333= 30.03mM

how would we describe doing this dilution. From the 30.0mM concentration we add 3.3333 mol per liter. As you see I am still confused. I have no way of asking her for explaination, so If any help could be proivded I would appreciate it.