The reason why the bulletin board notice feel nervous is: it was under a tack
In most common cases, the notice that is putted under a tack is intended to be displayed on the board for a pretty long time, highlighting the importance and the urgeny of the notice.
58 stamps is the number she gets each week. So if she went for one week, 58*1=58. 58*2=116 and so on. Because we don't know the exact number of weeks, we say 58w or 58*w because you multiply however many number of weeks she collects.
