Where can I find LR video explanations?

I'm working through some LR drills and going over my wrong answers, but can't seem to find video explanations for PT 3 Section 4, PT 15 Section 2, and PT A Section 4. Any ideas on where I can find them? I looked under the explanation videos tab and was able to find PT 3, but couldn't get videos for section 4 specifically. Same goes for the other PT videos I'm looking for :\