B3. Find all real solutions of the equation $\left(x^{2}+x+3\right)^{2}+3\left(x^{2}+x-1\right)=28$.
B3. We write the equation in the form $\left(x^{2}+x+3\right)^{2}+3\left(x^{2}+x+3\right)-40=0$ and introduce a new variable $u$ for the expression in parentheses. The equation $u^{2}+3 u-40=0$ has two solutions $u_{1}=-8$ and $u_{2}=5$. From this, we get two equations for $x$: $x^{2}+x+3=-8$, which has no solution, and $x^{2}+x+3=5$, which has two real solutions $x_{1}=-2$ and $x_{2}=1$.