Answer
$1090$
Work Step by Step
$S_{n}=\dfrac {n}{2}\left( 2a+\left( n-1\right) d\right) $
$a_{n}=a+\left( n-1\right) d\Rightarrow a_{1}=a+\left( 1-1\right) d=a=55$
$S_{n}=\dfrac {n}{2}\left( 2a+\left( n-1\right) d\right) =\dfrac {10}{2}\left( 2\times 55+\left( 10-1\right) \times 12\right) =1090$
