To compare fractions, you need a common denominator.
6 goes into 18 three times. If we multiply (5/6) by 3 on top and bottom you get
[tex]\frac{15}{18} [/tex]
Now we can compare numerators, since 15 > 13
[tex]\frac{5}{6} \ \textgreater \ \frac{13}{18}[/tex]