The question says that
can take
two positions for each value of
.
Consider the diagram for the specific case that
. Can you see why there can only be one location for
?
It's not unusual for more challenging questions in Maths exams for there to be a difficult-to-get mark that requires some detail to be recognised and addressed.
As a simple example, suppose that solving
was a 3 mark question:
- getting to
(x-4) \leqslant 0)
could be worth 1 mark
- translating that to
or 
could be the second mark
- recognising that
is excluded (as the original fraction was undefined) and thus the answer is )
or 
, could be the final mark
