\(ĐKXĐ:\)\(x\ne-1\)
\(B=\frac{x}{x+1}-\frac{3-3x}{x^2-x+1}+\frac{x+4}{x^3+1}\)
\(=\frac{x\left(x^2-x+1\right)}{x^3+1}-\frac{\left(3-3x\right)\left(x+1\right)}{x^3+1}+\frac{x+4}{x^3+1}\)
\(=\frac{x^3-x^2+x-3+3x^2+x+4}{x^3+1}\)
\(=\frac{x^3+2x^2+2x+1}{x^3+1}\)
\(=\frac{\left(x+1\right)\left(x^2+x+1\right)}{\left(x+1\right)\left(x^2-x+1\right)}\)
\(=\frac{x^2+x+1}{x^2-x+1}\)