Calculate the sum of the series sum_r=-18 (2r+3).

The summation is given by $\sum_{r=-1}^{8} (2r+3)$.
The index $r$ starts at $-1$ and goes up to 8.

For the first term, substitute $r=-1$:

For the last term, substitute $r=8$:

The number of terms is calculated as (upper limit - lower limit + 1):

There are 10 terms in this series.

Since the expression $2r+3$ is linear in $r$, this is an arithmetic series. The sum $S_n$ of an arithmetic series is given by:

Substitute the values of $n$, $a_1$, and $a_n$:

The sum is 100.