Answer: an = 6n - 15 (Choice C)
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Step-by-step explanation:
This sequence is arithmetic
The first term is a = -9
The common difference is d = 6 since we're adding 6 to each term to get the next one (eg: -3+6 = 3 or 3+6 = 9 or 9+6 = 15)
Plug those values into the arithmetic nth term formula below
an = a + d*(n-1)
an = -9 + 6*(n-1)
an = -9 + 6n-6
an = 6n - 15
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As a check, let's plug in something like n = 1
an = 6n - 15
a1 = 6*1 - 15
a1 = 6 - 15
a1 = -9
We see that the 1st term is -9, which matches the sequence given
Now let's plug in n = 2
an = 6n - 15
a2 = 6*2 - 15
a2 = 12 - 15
a2 = -3
The 2nd term is -3. This also matches.
I'll let you check the other values of n to confirm the answer.