Kudos to the LSAT writers. They've out done themselves with this question. I hope you didn't spend too much time getting this one wrong.
The passage is tough to understand. The writers make us think that a problem was solved when really, the problem still exists, just pushed one layer down. Crafty, crafty!
Let's pretend you're a painter name van Gogh. You're fucking awesome and you know it. Problem is, no one else knows it. But, alas, despite your god like skills with a brush, your body still needs mortal nourishment, clothing, and shelter. That means you need money. That means (because this is the stupid 1800's), you need to find a wealthy patron... who wants you to paint his ugly children. You'd like to not compromise your artistic genius, to not sell out, so to speak. But of course, that's a highly probably occurrence since no wealthy patron recognizes or agrees with your godly aesthetics.
Here's where the LSAT writers come to "the rescue". They say, "wait, the wealthy are dispersed among the various schools of art in roughly equal proportion to their percentage in the overall population". So no worries van Gogh. Just join up with one of those schools of art and you're all set. You know, maybe that one over there, on the corner with the flashing neon sign.
You see how this doesn't solve your problem? Previously, it's the patrons that you'd have to pander to. Now, it's the schools of art you'd have to pander to. What's the difference? You have to pander either way. The problem was not solved, just pushed one layer down.
But, of course, it certainly felt like it was solved when you were reading the original passage didn't it? Good job, LSAT writers.
This question plays off your presumption that once the nomads crossed the Bering land bridge into America, they didn't go back. Because why would anyone who made it to America want to go back to the god forsaken land of Siberia? No, thank you.
But of course, this was tens of thousands of years ago. Who knows. Maybe Siberia was awesome and they went back and forth for generations while the bridge was still around.
If that were the case, then the Clovis point could easily have been invented in America, carried with the nomads back over into Siberia, deposited and buried there for us to find thousands of years later.
If that's what happened, then finding a cache of Clovis points in Siberia doesn't suggest that it was invented in Siberia.
Of course, (A) also doesn't prove that it was invented in Siberia either. (A) in conjunction with the premise in the stimulus just makes it more likely that it was invented in Siberia.
That's all we're being asked to do in a Strengthen question.
The key to this question is understanding what an "effective hourly wage" means.
If you get paid a flat rate of $100, what's your "effective hourly wage"? Well, that depends on how many hours you worked. If you worked 1 hour, then you're "in effect" getting paid $100/hour. If you worked 10 hours, then you're "in effect" getting paid $10/hour.
Once you understand this, (B) should be obvious as the correct answer choice.