First, you need to have a common denominator for all of them, in this case, they can all go in 18 so that will be the common denominator.
\(\frac{7}{9} x \frac{2}{2} = \frac{14}{18}\)
\(\frac{5}{6} x \frac{3}{3} = \frac{15}{18}\)
\(\frac{2}{3} x \frac{6}{6} = \frac{12}{18}\)
\(\frac{13}{18}\)
Now you can tell which ones are the biggest or smallest. So from least to greatest you would have this.
\(\frac{2}{3} , \frac{13}{18} , \frac{7}{9} , \frac{5}{6}\)