Sure thing. Regarding the rate of profit, it’s something Roberts talks about a lot, so if you go to his website and search for “rate of profit”, you’ll find many articles (and graphs).

Regarding the extraction of surplus value, that one’s a little trickier. It’s a key part of what’s in volume 2 of Capital, specifically in chapter 6 (but the chapters before are important to comprehend as they build up to ch. 6). Long story short, it is only in the sphere of production (i.e. making things) where surplus value is created. So any costs that are not directly a part of production are “unproductive” and thus must be covered by surplus value. At the individual firm level this is often called “overhead” or “indirect costs”.

But at the economy level… what about the US? We don’t make anything anymore, so where is our surplus value coming from? Production in the global south! The value is created there but it is “imported” into the US. This is plainly obvious when you consider how much it costs to make a t-shirt in Bangladesh and what it ultimately sell for in the US. (I am admittedly mixing surplus value and profit a bit here but I think it’s appropriate).

How that surplus value makes it to workers indirectly is a bit abstract. But it can be done politically or through action. Meaning, you can pass a law that grants universal health care to pacify workers. Or the workers themselves can go on strike and earn more. Or even just through market forces this can happen. It’s a hard thing to empirically “prove” but it’s something you can see historically: when capital faces pressure, they have mechanisms to redistribute surplus value. In England, there was an increasingly militant labor movement that was eventually bought off by England ramping up imperialist plunder in the second half of the 19th century. In the US, up until the early 20th century you could always just steal more indigenous land and give it to workers (stealing capital and distributing it to workers isn’t the same and sharing surplus value per se but the effect is the same).