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
y[n]=0 , n<-10
y[n]=n+11, -10=<n<-1
y[n]=9-n, -1=<n=<8
y[n]=0, 8<n
TA Comments: Kim's solution is the right one. The solutions will be updated.
