Thank you for reporting, we will resolve it shortly
Q.
The area bounded by the curve $y=\sin \left(\frac{x}{3}\right), x$ - axis and lines $x=0$ and $x=3 \pi$ is
Solution:
Area $=\int\limits_{0}^{3 \pi} \sin \left(\frac{x}{3}\right) d x$
put $\frac{x}{3}=t$
$d x=3 \times d t$
$=\int\limits_{0}^{\pi} \sin t .3 d t\,x=0,3 \pi \Rightarrow t=0, \pi$
$=3(-\cos t)_{0}^{\pi}$
$=3[1+1]=6$ square units