Signs start with a negative and alternate, so the general term will have (-1)^n as a factor. The common difference has a magnitude of 5, so the general term is
\(a_{n}=(-1)^{n}\cdot (7+5(n-1))\)
and the sum is
\(\displaystyle S=\sum_{n=1}^{5}{(-1)^{n}\cdot (5n+2)}=-17\)
