[tex]a_1 = -7\\a_2 = -2\\r = a_2-a_1 = -2-(-7) =-2+7 = 5\\a_{n} = 608\\n = ?\\S_{n} = ?\\\\a_{n} = a_1+(n-1)r\\\\608=-7+(n-1)\cdot5\\\\608 = -7+5n-5\\\\608 = 5n-12\\\\5n = 608+12\\\\5n = 620 \ \ /:5\\\\\underline{n = 124}[/tex]
[tex]S_{n} = \frac{a_1+a_{n}}{2}\cdot n\\\\S_{124} = \frac{-7+608}{2}\cdot124\\\\S_{124} = 601\cdot62\\\\\boxed{S_{124} =37262}[/tex]
