I don’t have a copy of Preptest 82 yet. In general, I would say that many S/W questions work by eliminating or providing an alternate explanation, which leads one to trust or distrust the passage’s conclusion more. The passages are often written as asserting one possible conclusion. For example:
My student got a 172 on the most recent LSAT. Therefore, I’m a great LSAT tutor.
I’ve seized on one possible explanation for the score – my tutoring. But if you can think of another (maybe he was scoring really well before we started working together) then you have the basis for a good strengthen OR weaken question – providing or eliminating that explanation.
Good Weaken Q answer:
My student was scoring 150 on practice tests before we starting working together.
Good Strengthen Q answer:
My student was scoring 172 on practice tests before we started working together.
Sorry, I can’t give you a more specific answer without seeing the actual questions.