A school exports its mark book as one long list. Student 0's marks come first, one for each of the num_tests tests, then student 1's marks, and so on.
A student makes the honour roll when both of these are true:
cutoff,50.Task: write honour_roll(marks, num_tests, cutoff) and return the positions of the students on the honour roll, as a plain list, smallest first. Students are counted from 0.
If the marks don't split evenly into rows of num_tests, the export is broken. Return None.
There is always at least one mark, and num_tests is at least 1. Don't round the averages before comparing.