Find ${\displaystyle \underset{0}{\overset{6}{}}}f(x)dx$ for each graph of $y=f(x),$ where $f(x)$ consists of line segments and circular arcs.

a$.{\displaystyle \underset{0}{\overset{6}{}}}f(x)dx=$

$($Type an exact answer, using $$ as needed.$)$

b$.{\displaystyle \underset{0}{\overset{6}{}}}f(x)dx=$

$($Type an exact answer, using $$ as needed.$)$