Example 5. Find the distance from the point $A(2,3,-4)$ to the plane $2 x+6 y-3 z+16=0$.
Solution. By the formula of item $7^{\circ}$, we have

$$
d=\frac{|2 \cdot 2+6 \cdot 3-3(-4)+16|}{\sqrt{4+36+9}}=7 \frac{1}{7}
$$

Answer. $d=7 \frac{1}{7}$.