[填空题]
$\text { The following diagram shows the graph of } f(x)=\frac{4 x}{x^{2}+1} \text {, for } 0 \leq x \leq 6 \text {, and the line } x=6 \text {. }$
Let R be the region enclosed by the graph of f , the x -axis and the line x=6 . Find the area of R .
