can someone tell me how to do it, i have more problems like this

Answer:
[tex]\large\boxed{\dfrac{7n}{30}=\dfrac{7}{30}n}[/tex]
Step-by-step explanation:
[tex]\dfrac{2n}{5}+\left(-\dfrac{n}{6}\right)=\dfrac{2n}{5}-\dfrac{n}{6}[/tex]
To subtract both fractions we need a common denominator.
[tex]LCD=(5)(6)=30[/tex]
[tex]\dfrac{2n}{5}=\dfrac{2n\cdot6}{5\cdot6}=\dfrac{12n}{30}\\\\\dfrac{n}{6}=\dfrac{n\cdot5}{6\cdot5}=\dfrac{5n}{30}[/tex]
Therfore
[tex]\dfrac{2n}{5}-\dfrac{n}{6}=\dfrac{12n}{30}-\dfrac{5n}{30}=\dfrac{12n-5n}{30}=\dfrac{7n}{30}=\dfrac{7}{30}n[/tex]