For a curve $f(x)=x^{2}-2x, x \in [-1,3]$:
a. Find

$$\int_{-1}^{3} f(x) dx\text{.}$$

b. Sketch the graph of $f(x)$ and shade the area bounded by $x$-axis and the curve $f(x)$.
c. Find the area bounded by $x$-axis and the curve $f(x)$.