Ask four questions.
1. Does the second part state a purpose, a result/reaction, or an endpoint?
2. Which particle expresses that relationship: كَيْ، إِذَنْ، حَتَّى، لِ?
3. Which imperfect follows, and which ending group is it in?
4. Is any visible nūn actually an inflectional nūn, or a different nūn?
Do not decide from one word alone; read the complete sentence.