Resposta:

[tex]\textsf{Leia abaixo}[/tex]

Explicação passo a passo:

[tex]\mathsf{S_n = \dfrac{(a_1 + a_n)n}{2}}[/tex]

[tex]\mathsf{S_8 = \dfrac{(a_1 + a_8)8}{2}}[/tex]

[tex]\mathsf{S_8 = \dfrac{(a_1 + a_1 + 7r)8}{2}}[/tex]

[tex]\mathsf{60 = \dfrac{(-10 -10 + 7r)8}{2}}[/tex]

[tex]\mathsf{7r - 20 = 15}[/tex]

[tex]\mathsf{7r = 35}[/tex]

[tex]\boxed{\boxed{\mathsf{r = 5}}}[/tex]

[tex]\mathsf{a_n = a_1 + (n - 1)r}[/tex]

[tex]\mathsf{a_8 = -10 + (8 - 1)5}[/tex]

[tex]\mathsf{a_8 = -10 + (7)5}[/tex]

[tex]\mathsf{a_8 = 35 -10}[/tex]

[tex]\boxed{\boxed{\mathsf{a_8 = 25}}}\leftarrow\textsf{letra A}[/tex]