To find out, you can write the ratios as a fraction and simplify, like this
[tex]\begin{gathered} 7\colon3\text{ }\Leftrightarrow\frac{7}{3} \\ 28\colon12\Leftrightarrow\frac{28}{12} \\ \text{Now simplifying the second ratio} \\ \frac{28}{12}=\frac{4\cdot7}{4\cdot3}=\frac{7}{3} \\ \end{gathered}[/tex]