Critical Reasoning OG 96

[doshspy]

I have read and re-read the solution to OG 96 and don't understand it.
Originally I thought it was a Type 4(alternate mode of causation problem) but that doesn't seem right and I can't wrap my head around the the assumption that the commentator makes to solve the problem. I just don't see how it works.

Thanks!!

[StaceyKoprince]

Please post the actual question so we can respond. Thanks!