[m]a_{1}=10[/m]
[m]a_{2}=6[/m] ⇒ [m]a_{2}=a_{1}+d [/m] ⇒ [m]d=a_{2}-a_{1}[/m]
[m]d=6-10=-4[/m]
n=16
[m]a_{16}=10+(-4)\cdot (16-1)[/m]
[m]a_{16}=10-60[/m]
[m]a_{16}=-50[/m]
[m]S_{n}=\frac{2a_{1}+d\cdot (n-1)}{2}[/m]
[m]S_{30}=\frac{2\cdot 10+(-4)\cdot (30-1)}{2}[/m]
[m]S_{30}=\frac{20-116}{2}[/m]
[m]S_{30}=-48[/m]