3n - 5p + 2n = 10p
Since we are solving for n, you want to have all the terms containing the variable n on the left side of the equation and everything else on the right side.
Let's do this by adding 5p to both sides.
3n + 2n = 10p + 5p
Now combine like terms.
5n = 15p
Divide both sides by 5 since we are solving for the variable n.
n = 3p