It involves counting in binary, which I'm pretty sure isn't in this syllabus, but basically:
000 = 0
001 = 1
010 = 2
011 = 3
100 = 4
and so on until it reaches the maximum value for 3 bits which is 111 = 7.
For this question it asks you to take a look at 2, 3 and 4 seconds and it samples it at...