Looking for suggested solutions of Q4ab and Q2bc. Please explain more about how to get the answer of Q4a. Thank you. (The system says my question is...

Looking for suggested solutions of Q4ab and Q2bc. Please explain more about how to get the answer of Q4a. Thank you.

(The system says my question is too short, but I think that is enough. So just ignore the words in this parenthesis :p)

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