Plumbing advice

Hi folks. So we got a bit of a slow leakage in our kitchen ceiling which has a bathroom right above it. I pulled out the moist drywall and realized It's the drain line from the bath tub that is the root cause. It's PVC somehow connected to cast iron. Pics attached. Can anyone advise what parts I would need to fix this? My research tells me I need a shielded coupling. I'm just not sure how is this PVC originally connected to CI. And if I remove it will a fernco coupling work as the CI outside diameter is larger than the PVC inserted into it. I'm fond of such project and want to do it myself. Also the CI joint is dry. It's the fitting with debris on it that has leakage. Also I think the PVC is 3 inch. Thanks in advance for your guidance. Also I have additional pics if needed.