Let $p$ be the number of all triangles that can be formed by joining the vertices of a regular $n$-gon $P$, and $q$ be the number of all quadrilaterals that can be formed by joining the vertices of $P$. If $p+q=126$, then the eccentricity of the ellipse $\dfrac{x^2}{16}+\dfrac{y^2}{n}=1$ is: