Evaluate the following integrals:

$($i$){\displaystyle \underset{2}{\overset{6}{}}}(3x^2-2x-1)(x-3)dx$

$($ii$){\displaystyle \underset{0}{\overset{5}{}}}cosx(x-)dx$

$($iii$){\displaystyle \underset{0}{\overset{3}{}}}{x}^3(x+1)dx$

$($iv$){\displaystyle \underset{-1}{\overset{1}{}}}{x}^2(3x+1)dx$