TeX source:
\begin{array}{ccl} \genfrac{}{}{1pt}{}{\dfrac{x+7}{2}}{\dfrac{8}{y-1}} &=& \dfrac{x+7}{2} : \dfrac{8}{y-1} \cr\cr &=& \dfrac{x+7}{2} \cdot \dfrac{y-1}{8} \cr\cr &=& \dfrac{\left(x+7\right)\left(y-1\right)}{2\cdot 8} \cr\cr &=& \dfrac{xy-x+7y-7}{16} \end{array}