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Expressing work as a riemann sum

I've attached a picture of the problem I'm working on. Now I know work is either force times distance or the integral from a to b of f(x)dx, and that F=kx, but it seems like with the information they give me in this problem there isn't enough to find any of the three!

I AM new to this type of problem and my professor kind of brushed over the topic very quickly so I don't feel very confident in it, if someone could point me in the right direction on one or two of these problems I think I'd be OK to do the rest myself. Thanks in advance!