My book tells me the answer to part b is [itex]1.96*10^5[/itex], but I fail to see where I have gone wrong with this?
Fair comment about the units. I don't bother to add them in when I'm doing questions like this until I get something wrong, or if I'm presenting it in, say, an exam. However this clearly wasn't an issue of unit conversion, because there are none. All the given figures are in metres, they stay in metres, and the answer at the end has units of N/m.There are many units missing, or wrong units. I would guess one cm<->m-conversion went wrong, but it is hard to tell if you do not add units.