24. Problem 12.11
25. Estimate the minimum Jeans mass reached by a collapsing 1,500 Solar mass cloud
26. Problem 13.1
27. Problem 13.6. Compare to Problem 11.2.
28. Problem 13.7
29. What is the Helim Flash? Why does it occur? Why does it happen only for stars with mass < 2.25 Solar masses (book gives limit 1.8 or so solar masses)?