Answer
$\dfrac{1}{2}$
Work Step by Step
The fractions are not similar since they have different fractions.
Make the fractions similar using their LCD of $18$.
$\dfrac{13}{18} - \dfrac{2}{9}
\\=\dfrac{13}{18}-\dfrac{2\color{blue}{(2)}}{9\color{blue}{(2)}}
\\=\dfrac{13}{18}-\dfrac{4}{18}$
Now that the fractions are similar, subtract the numerators and copy the denominator to obtain:
$=\dfrac{13-4}{18}
\\=\dfrac{9}{18}
\\=\dfrac{1}{2}$
