A geometric sequence has first term 3 and common ratio 2. What is the 6th term?

In a geometric sequence $a_n=a_1r^{n-1}$. With $a_1=3$ and $r=2$, the sixth term is $a_6=3\cdot2^5=3\cdot32=96$, choice C. Listing terms confirms it: $3, 6, 12, 24, 48, 96$. Choice D ($192$) uses an exponent of $6$ instead of $5$, which is the seventh term. Choice B ($36$) is $3\cdot12$ or $6\cdot6$, which does not follow the pattern. Choice A ($18$) is $3\cdot6$, treating the sequence as arithmetic-style multiplication by the term number. Remember that the exponent is one less than the term number.