Consider two functions $f$ and $gon2,7$ such that ${\displaystyle \underset{2}{\overset{7}{}}}f(x)dx=11,{\displaystyle \underset{2}{\overset{7}{}}}g(x)dx=7,{\displaystyle \underset{6}{\overset{7}{}}}f(x)dx=5,$ and ${\displaystyle \underset{2}{\overset{6}{}}}g(x)dx=4.$ Evaluate the following integrals.

$a.{\displaystyle \underset{2}{\overset{6}{}}}2f(x)dx=12(Simplify$ your answer.$)$

$b.{\displaystyle \underset{2}{\overset{7}{}}}(f(x)-g(x))dx=,(Simplify$ your answer.$)$