(a) Invert the value of the Hubble constant calculated in Exercise 12
above.  What is the age of the universe (the "Hubble time")
as predicted by Hubble and Humason's results?

(b) Now invert the value of the Hubble constant calculated in Exercise 13.
What is the Hubble time predicted by these modern results?

(c) If you did the problems correctly, Hubble and Humason's results are
very different from the modern results.  Why, if their numbers were so far 
off, do we still credit Edwin Hubble and his collaborators for the discovery
of the expansion of the universe?  This is actually a pretty important point
when it comes to the process of scientific discovery, so think about it...