Aliasing Responses

These are my attempts for these problems. I still need to tackle some of part b). I am not sure about the discrete responses for Y_d(e^jΩ) of b)i).
I appreciate some guidance or maybe some good sources. Also I am finding b) ii) a bit confusing when it asks "Determine and draw the new specifications for H_d (e^j^W) such that Y_d (e^j^W) remains as determined in (a)(ii) above." If in a), H_d (e^j^W) already filtered from pi/2 onwards, why should there be new specifcations to obtain the same Y_d (e^j^W) as in a) ii) ? thanks

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