[Algebra]
Problem: Determine all values of $x$ for which $\frac{x^{2}+x+4}{2 x+1}=\frac{4}{x}$.

Solution: Manipulating the given equation and noting that $x \neq 0$ and $x \neq-\frac{1}{2}$ since neither denominator can equal 0 , we obtain

$$
\begin{aligned}
\frac{x^{2}+x+4}{2 x+1} & =\frac{4}{x} \\
x\left(x^{2}+x+4\right) & =4(2 x+1) \\
x^{3}+x^{2}+4 x & =8 x+4 \\
x^{3}+x^{2}-4 x-4 & =0 \\
x^{2}(x+1)-4(x+1) & =0 \\
(x+1)\left(x^{2}-4\right) & =0 \\
(x+1)(x-2)(x+2) & =0
\end{aligned}
$$

Therefore, $x=-1$ or $x=2$ or $x=-2$. We can check by substitution that each satisfies the original equation.

Final answer: $-1$,$2$,$-2$