Law of Restitution: Collisions and inequality of e.

...

Here's the question.

The part which I want is specific to part 6(b)


I have showed that $e > \displaystyle\frac{1}{4}$, however I can't seem to think of why it would be $e < \displaystyle\frac{9}{16}$ too.

Here's the mark scheme, and weirdly, it doesn't talk about the second tail of the inequality.
Question 6(b) of the mark scheme is what you want.

http://pmt.physicsandmathstutor.com/download/Maths/A-level/M2/Topic-Qs/Edexcel-Set-1/M2%20Collisions%20-%20Successive%20impacts.pdf

The markscheme you've referenced is an Edexcel Internal Review document, and as such has errors - and seems to have been propagated across a few sites.

The original question was used in the June 2006 M2 exam, and here's the markscheme from that:

As you can see the the (9/16)e restriction comes from the inequality that is given in both!