First, please remember to cite the source of any problem you post. I'll have to discuss this one in somewhat general terms because the author is not cited.

On the first one, it is the case that the infinitive can be used to indicate an objective or it can indicate the meaning "in order to <do something>" - but it really depends on the sentence. That's tricky.

On the second one, it is the case that somethign does lead to <something else> but we don't actually have an infinitive (at least, not in the option that you showed), so this is a different set-up.

Here's the general process for any SC question:
1. Read the original sentence all the way through.
2. If you happen to spot anything problematic, examine. If it's an error, cross off A. Then scan the other choices vertically, at the same point as that error you found (do NOT read the whole answer choice), and cross off any others that repeat the same error. If you're not sure, don't panic, don't think you "have" to figure something out here - just leave choice A in and move on to step 4.
3 .Repeat the above until you've dealt with everything you happened to see (AND you know how to deal with!) on your first read-through of the original sentence (note: sometimes you won't see anything on the first read-through).
4. Then, do a vertical scan of the first word of each choice. If you can identify the potential error based on the differences you see, deal with it. If not, do a vertical scan of the last word of each choice - same thing. After that, do a vertical scan starting at the beginning of each choice.
5. If you notice a difference when scanning but you don't know what error that difference might signify, keep going - look for a different split.
6. If you've dealt with everything you know how to deal with and you still have more than one choice left, pick something and move on. Don't agonize over it - just pick and go.

Did you ever try the SC "cheat sheet clues" list strategy I mentioned in an earlier post? If so, how did that work for you? If not, try it. If you get good with this, it's like reading a math problem: you see a certain symbol and you know that you should be thinking about <fill in the blank>. You see "!" and you know that means "factorial" and then you have an idea of what you need to do for at least part of the problem. Make SC more like that - you see certain differences among the different answer choices, and then that tells you which rules are being tested.

Also, DO NOT ever feel that you "must" know how to deal with everything you see. You don't have to, most of the time If you see something and you're not sure what to do, just look for something else. These problems almost always have 4 or 5 things you can look at - just keep making comparisons among the different answers to find differences, and then deal with any differences that you know. It's very common for me to see a difference and think, "Hmm, I don't like that one; I'd rather find something that's easier / more straightforward for me" and then I go find something else and deal with that.

Identify some good source for RC. (I obviously like our books, but I'm also obviously biased - so ask around. )

For very short passages, the primary difficulty usually has to do with very dense sentences and a lack of transitions (transitions are the in-between sentences that smooth the transition to different points or messages) - the lack of transitions just serves to make the whole thing even more dense. We do have a section in our book that helps you learn how to read and "unpack" very complex, dense material. (Sadly, I can't just copy and paste that section of the book here...)

Good luck - let us know how it goes!