Hello, viet!
I assume this is a Calculus problem . . .
A ball of radius 15 has a round hole of radius 8 drilled through its center.
Find the volume of the resulting solid. Code:
15
* * *
*::::::::::*
*::::::::::::::*
*   8+    *P

*  *
  *     +     *  
*  *15

*  *
*  *
*  *
* * *

The circle has equation: .$\displaystyle x^2 + y^2 \:=\:225\quad\Rightarrow\quad y \:=\:\pm\sqrt{225x^2}$
The region between the circle and $\displaystyle y = 8$ is revolved about the xaxis.
The coordinates of point $\displaystyle P$ are: .$\displaystyle \left(\sqrt{161},\,8\right)$
The volume of revolution is: .$\displaystyle V \;= \; 2 \times \pi\int^{\sqrt{161}}_0\left[(225  x^2)  8^2\right]\,dx$