69 Valiant cyl4 not firing?

Hi, I am new, I bought a 69 Valiant 100, 225 six. It runs on 5 cyl. Cylinder 4 does not fire, could this be cam, burned valves, rings?

I paid $500 for car. 82K on it original, car was garaged and is rust free. Owner crazy about oiling the whole car.... it drips. No Rust anywhere, so I figured I would fix the engine. Hopefully it only needs a valve/head job.

Help!