$(4pts)$ Evaluate the following double integrals.

$(a){\displaystyle \underset{R}{\overset{\phantom{}}{}}}sin(x+y)dA,$ where $Ris$ the rectangular region $0x\frac{}{4},0y\frac{}{2}.$

$(b){\displaystyle \underset{R}{\overset{\phantom{}}{}}}f(x,y)dA,$ where $f(x,y)=1$ and $Ris$ the disk $(x-1{)}^2+(y-2{)}^{2}9.$

$(3pts)$ Evaluate the integral $by$ reversing the order $of$ integration.

${\displaystyle \underset{0}{\overset{1}{}}}{\displaystyle \underset{\sqrt[\phantom{2}]{y}}{\overset{1}{}}}cos(1+x^3)dxdy$