Recently, I am studying the book Character Theory and the McKay Conjecture. I am trying to solve the following exercise:

(Exercise 5.9)

Let $N\unlhd G$, and suppose that $\theta\in\rm Irr(N)$ is $G$-invariant. If $G/N=Q_8$ show that θ extends to G. ( Hint : We may assume that $N\subseteq Z(G)$ and that $\theta$ is faithful. Write $Z/N=Z(G/N)$,$G/N=<Nx, Ny>$ with $Nx^2=Ny^2$ of order $2$. Show that $Z\subseteq Z(G)$ and that $G'\cap N=1$, by proving that $[x,y]^2=1$.)

I know how to prove this hint,but I can't use it to solve this question.