[tex]\begin{gathered} AB\colon RS\to\frac{AB}{RS}=\frac{2}{1} \\ BC\colon ST\to\frac{BC}{ST}=\frac{4}{2} \end{gathered}[/tex]
or:
[tex]\begin{gathered} AB\colon RS\to\frac{AB}{RS}=\frac{6}{3} \\ BC\colon ST\to\frac{BC}{ST}=\frac{12}{6} \end{gathered}[/tex]
