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

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Abstract algebra continues the conceptual developments of linear algebra, on an even grander scale.

Dr. Paul Garrett