It seems as if it adds 2 blocks to the bottom end each time, and 1 to the top.
So, it would be a t-shape with those rules
This question is impossible to answer without knowing or being able to see the question.
The common ratio (R) is -3.
-2 times -3 is 6.
6 times -3 is -18.
-18 times -3 is 54.
R=-3.
This is a geometric sequence.