how does (x/y)/((w+z)+(a+b)) simplify down to (bxz)/(y(bw+az)?

[tex] \dfrac{\dfrac{x}{y}}{\dfrac{w}{z}+\dfrac{a}{b}}=\\\\\\
\dfrac{\dfrac{x}{y}}{\dfrac{bw}{bz}+\dfrac{az}{bz}}=\\\\\\
\dfrac{\dfrac{x}{y}}{\dfrac{bw+az}{bz}}=\\\\\\
\dfrac{x}{y}\cdot\dfrac{bz}{bw+az}=\\\\\\
\dfrac{bxz}{y(bw+az)}
[/tex]