Hey there!
Ratios can also be expressed as fractions. The first number will be your numerator while the second number will be your denominator.
[tex]7:3 = \frac{7}{3} =2 \frac{1}{3} [/tex]
[tex]8:4 = \frac{8}{4} = 2[/tex]
[tex]9:5 = \frac{9}{5} = 1 \frac{4}{5} [/tex]
[tex]2:7 = \frac{2}{7} [/tex]
You could then divide these fractions out by dividing the numerator by the denominator to see which is the largest, but we can already tell that 2 1/3, or 7:3, will be the largest, since none of the other fractions are that large.
Hope this helped you out! :-)