How do you find the sum of the arithmetic series Sigma(42-9k) from k=7 to 11?

$- 195$
$\sum \left(42 - 9 k\right)$ from $k = 7$ to $11$ is a math problem. It is basically saying, starting when $k$ equals $7$ solve the expression of $42 - 9 k$. Then, add that value to when $k = 8$, $k = 9$, $k = 10$ and $k = 11$. Here's what that looks like:
$\left(42 - 9 \cdot 7\right) + \left(42 - 9 \cdot 8\right) + \left(42 - 9 \cdot 9\right) + \left(42 - 9 \cdot 10\right) + \left(42 - 9 \cdot 11\right)$. This can be simplified to $- 21 + - 30 + - 39 + - 48 + - 57$, which is $- 195$.