3. Solve the equation:
$$
(6 x+7)^{2}(3 x+4)(x+1)=6 \text {. }
$$
$$
\begin{array}{l}
(6 x+7)^{2}(6 x+8)(6 x+6)=72, \\
\text { i.e. }\left(36 x^{2}+84 x+49\right)\left(36 x^{2}+84 x+48\right)=72 .
\end{array}
$$

Answer: $x_{1}=-\frac{2}{3}, x_{2}=-\frac{5}{3}$.