Answer
$$
f(x)=3 x+1
$$
$$
x_{1}=-1, x_{2}=0, x_{3}=1 , x_{4}=2, x_{5}=3 \\
f\left(x_{1}\right)=3 (-1)+1=-2, \,\,\, f\left(x_{2}\right)=3 (0)+1=1, \\ f\left(x_{3}\right)=3 (1)+1=4 , \,\,\, f\left(x_{4}\right)=7, f\left(x_{5}\right)=10 $$
$$
\begin{aligned}
\sum_{i=1}^{5} f\left(x_{i}\right) &=f(x_1)+f(x_2)+f(x_3)+f(x_4)+f(x_5) \\
&=-2+1+4+7+10 \\
& =20
\end{aligned}
$$
Work Step by Step
$$
f(x)=3 x+1
$$
$$
x_{1}=-1, x_{2}=0, x_{3}=1 , x_{4}=2, x_{5}=3 \\
f\left(x_{1}\right)=3 (-1)+1=-2, \,\,\, f\left(x_{2}\right)=3 (0)+1=1, \\ f\left(x_{3}\right)=3 (1)+1=4 , \,\,\, f\left(x_{4}\right)=7, f\left(x_{5}\right)=10 $$
$$
\begin{aligned}
\sum_{i=1}^{5} f\left(x_{i}\right) &=f(x_1)+f(x_2)+f(x_3)+f(x_4)+f(x_5) \\
&=-2+1+4+7+10 \\
& =20
\end{aligned}
$$
