Chapter 5.2, Problem 75E

In the following exercises, evaluate the double integral ${\displaystyle \underset{D}{\iint }f\left(x,y\right)dA}$over the region D.
75. $f\left(x,y\right)=1$ and $D=\left\{\left(x,y\right)|0\le x\le \frac{\pi }{2},\sin x\le y\le 1+\sin x\right\}$