I have been given this equation.

$\displaystyle \Pi_t=\gamma\Pi_t+(1-\gamma)\Pi_{t-1}-\alpha(u_t-u_n)$

And told it can be rearranged to get this.

$\displaystyle \Pi_t=\Pi_{t-1}-\frac{\alpha(u_t-u_n)}{(1-\gamma)}$

I don't understand how they got this. It's off my lecture slides.

Could someone please enlighten me?