H.W 7 - tpd and trees

1.In h.w 7 question no. 4 we are asked to describe an AND’s gates values and unstable intervals. One thing I’m not sure about is when one of the inputs becomes unstable it means that at the same moment the input becomes also unstable? (that what we have in all the choices in the multiple choice question, x1 becomes unstable at t=5 and all the options indicate
that y becomes unstable at t=5).
2. In the claim about balanced partitions slide 16 of the lecture we have an example of n =13 and the k we choose for 2^4 is 4 is it because we are looking for the minimal k that will help us bound r and because eventually k stands for the minimal depth?

one question per post please. with an informative title (not hw number, but topic)