7.5c sanity check

- Find a counterexample to show that discussion manual problem 7.5c would be false if the numbers 61 and 10 were replaced by 19 and 3. (That is, disprove the following claim: "A software engineer slept for 19 hours over 3 nights. Assuming that the engineer sleeps precisely an integer number of hours each night show that on some pair of consecutive nights she slept at least 13 hours.")

- Make sure that your proof for 7.5c can not be easily adapted into a proof of the false statement above. (If it can, then your original proof also has a flaw; try to find it.)