Kate's proofreading fixes

[k8hertweck]

A few changes here based on proofreading from Greg's render of #614:

• updated figure 8.3 pdf so it matches png and stg
• typo correction in solutions
• pg 405 title for exercise 10.8.4 is separated from answer
• pg 154 exercise 6.11.8 answer 3 formatting

[k8hertweck]

I did a local rebase against #614 and re-rendered; it looks like my changes don't cause any more issues in the rest of the chapters affected.