Using primitive or derived rules abiding to system expressed in Beginning Logic by E.Lemmon, prove the following sequent.

Using primitive or derived rules abiding to system expressed in Beginning Logic by E.J.Lemmon, prove the following sequent. I need help seeing what to assume and how that should be assumed as oppsed to something else in order to get the solution.

├ (P & Q → - R) → (P → - (Q & R))