EL7 Tweaks

[siwelwerd]

• Activity 5.7.2 Maybe an <aside> saying that this is Newton's Law of Heating and Cooling?
• Activity 5.7.5 An extra sentence of context at the beginning might be helpful, along the lines of "The concentration of salt in ocean water, called salinity, varies as you go deeper in the ocean."
• Activity 5.7.6 I think this is my fault, A_0 should be a subscript. Maybe just stick it in math mode. Also, maybe an aside that this is 12 tone equal temperament, but there are many other temperaments.
• Activity 5.7.10(a)The percent is split over a line break. I suspect this is because it isn't in math mode. Put it inside the math mode, but escape it with a \.
• Related to a comment I made in #295, maybe 5.7.8 and Remark 5.7.11 can be expanded to cover continuous compounding as a motivation for $e$.

[tdegeorge]

I believe I fixed everything except the motivation for e part....Figured we could talk about that as a group. I am not sure how much to put in there.