Answer
$612$
Work Step by Step
We will use the formula for the sum of the first $n$ terms of an arithmetic sequence, which is given as:
$$S_n=\dfrac{n}{2}[2a_1+(n-1)d]$$
With $a_2=6$ and $d=10$, we solve for the first term to obtain:
$$a_1=a_2-d=6-10=-4$$
Then we use the formula above to find the sum of the first $12$ terms of the sequence:
$$S_{12}=\dfrac{12}{2}[(2)(-4)+(11)(10)]=6 \times 102 =612$$
