Answer
$${S_{12}} = 612$$
Work Step by Step
$$\eqalign{
& {a_2} = 6,\,\,d = 10 \cr
& d = {a_2} - {a_1} \cr
& {a_1} = {a_2} - d \cr
& {a_1} = 6 - 10 \cr
& {a_1} = - 4 \cr
& {\text{Calculate }}{S_{12}},{\text{ use }}{S_n} = \frac{n}{2}\left[ {2{a_1} + \left( {n - 1} \right)d} \right]{\text{ with }}n = 12 \cr
& {S_{12}} = \frac{{12}}{2}\left[ {2\left( { - 4} \right) + \left( {12 - 1} \right)\left( {10} \right)} \right] \cr
& {\text{Simplifying}} \cr
& {S_{12}} = 6\left[ { - 8 + 110} \right] \cr
& {S_{12}} = 612 \cr} $$
