You're correct! Great job :)
Remember the vertical angle theorem states that for two lines that cross each other, the angles that are right across from each other are equal (see the 1st picture).
From your picture, 2n and the angle beside it must add up to 90° (marked in green in 2nd attached picture). The angle beside it, using the vertical angle theorem must be equal to (n+18)°. That means 90 - 2n = n+18 (or 90 - (n+18) = 2n, either works). Solve for n:
[tex]90 - 2n = n+18\\
90 = 3n + 18\\ 72 = 3n\\ n = 24[/tex]
