This is tricky because it has a lot of variables, but we just have to treat this problem normally.
[tex]yp+yn=x[/tex]
separate y from p + n (feel free to check that you can do this by multiplying y out again and seeing that we have the same thing as before)
[tex]y(p+n)=x[/tex]
divide p + n on both sides
[tex]y = \frac{x}{p+n}[/tex]
Answer:
[tex]y = \frac{x}{p+n}[/tex]