Answer
$\dfrac{5}{42}$
Work Step by Step
Find the LCM (lease common multiple) of the denominators:
$14 = 7(2)
\\21=7(3)$
The LCM is $7(2)(3) = 42$
Thus, the LCD is also $42$
Make the fractions similar using their LCD to obtain:
$=\dfrac{3(3)}{14(3)} - \dfrac{2(2)}{21(2)}
\\=\dfrac{9}{42}-\dfrac{4}{42}
\\=\dfrac{9-4}{42}
\\=\dfrac{5}{42}$
