#### Answer

neither

#### Work Step by Step

In order for a sequence to be geometric, the quotient of all consecutive terms must be constant.
Hence here: $\frac{c_{2}}{c_1}=\frac{12}{6}=2\ne\frac{c_{3}}{c_2}=\frac{36}{12}=3$, which is not constant thus it is not a geometric sequence.
In order for a sequence to be arithmetic, the difference of all consecutive terms must be constant.
Hence here: $c_{2}-c_1=12-6=6\ne c_3-c_2=36-12=24$, which is not constant thus it is not an arithmetic sequence.
Hence it is neither.