343. Solve the equation:

$$
x \frac{19-x}{x+1}\left(x+\frac{19-x}{x+1}\right)=84
$$
$\triangle$ Let $\frac{19-x}{x+1}=y$. Then

$$
x y(x+y)=84
$$

In addition, transform the equality with the substitution:

$$
19-x=x y+y, \quad x+y+x y=19
$$

This results in a symmetric system of equations:

$$
x y(x+y)=84, \quad x+y+x y=19
$$

Complete the solution on your own.

Answer: $3,4,6 \pm \sqrt{29}$.