\(B=\dfrac{x}{y}\cdot\dfrac{1}{2z}\cdot xyz\cdot\left(\dfrac{x^3}{yz^2}+y\right)\)
\(=\dfrac{x^2yz}{2yz}\cdot\dfrac{x^3+y^2z^2}{yz^2}\)
\(=\dfrac{x^2}{2}\cdot\dfrac{1}{yz^2}\cdot\left(x^3+y^2z^2\right)=\dfrac{x^2}{2yz^2}\cdot\left(x^3+y^2z^2\right)\)