Answer
$-2325$
Work Step by Step
Sum of first $n$th term of an arithmetic sequence can be calculated as:
$S_n=\dfrac{n}{2}[a_1+a_n]$
since, we have {$-5,-10,-15,..., -150$}
This implies that $a_1=-5,a_n=-150,n=30$
Now,
$S_{30}=\dfrac{30}{2}[-5+(-150)]=-2325$
