Divide 3 first, which can be considered as 3 times the volume of the ball.

Then the triple integral of x+y is processed and the spherical coordinate system is recommended.

Use x=rsinαcosθ.

y=rsinαsinθ

Then it becomes (rsin α cos θ+rsin α sin θ) r2sin α drd α d θ.

The specific meaning of the symbol is in the book, which can be reviewed. After all, this formula is often used.