Notes on problems 4.1-4.12 in chapter 4: 4.6 should say "(4.12)" instead of
"(4.6)". Also: consider 4.8 and part (b) of 4.10 as optional; note that
4.1 is just a plug-into-formula problem, and 4.2 is only calculus.
Finally, 4.11 refers (of course) to Model II.
Solutions are here.