Answer
a) Please see the image.
b) This suggests that the number of cells in the female gametophyte and the ploidy of endosperm has varied during the early history of the flowering plants, and it is not clear (other trees could be drawn from the same data) what the ancestral state was.
Work Step by Step
Please note that the image in the answer shown here differs from that in the book— there are multiple ways to draw the tree, and this one is more parsimonious (see an earlier chapter on why this is preferred in phylogenies).
