Question: the answer to this question is c19h28o2 when i apply...

the answer to this question is C19H28O2.

when I apply the rule of 13 I get
C22
C21H12 (taking away a carbon and adding a hydrogen)
C20H24 (same as second step)
C19H20O (taking away carbon and 4 hydrogen and adding an Oxygen)
C18H16O2 (taking away another carbon and 4 hydrogens to add another oxygen)

as stated above, the answer is C19H28O2.

am I applying the rule of 13 incorrectly?