I think TA's solution #3.b is wrong.
I think the graph of x[n-k] is wrong.
X-axis should represent n+1, n+2, n+3, ...., n+10.
So, the answer should be
0 , n<-10 n+11, -10=<n<-1 9-n, -1=<n=<8 0, 8<n
