Answer
90
Work Step by Step
$S_{n}=\dfrac {2a_{1}+\left( n-1\right) d}{2}\times n;d=\left( -1\right) -\left( -5\right) =\left( -5\right) -\left( -9\right) =4\Rightarrow S_{10}=\dfrac {2\times \left( -9\right) +\left( 10-1\right) \times 4}{2}\times 10=90$
