The question 2a asks how many complete loops were made. This has to be a whole number. So, if 15/T is not a whole number (which it isn't) we need to take the nearest whole number less than this. That is what the floor function does.
For 2b, we see that 15/T is 22.5, which means the passenger does 22 complete loops, plus half of a loop. Since the passenger starts at the bottom, 22 complete loops will leave him/her at the bottom, and another half loop will take them to the top.