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Answer:
The choice 4 and 6 ;
[tex]7i(7i)[/tex]
and
[tex](9 + 3i)(9 - 3i)[/tex]
Step-by-step explanation:
[tex]7i(7i) = 49 {i}^{2} = - 49[/tex]
__o_o__
[tex](9 + 3i)(9 - 3i) \\ = 81 - 27i + 27i - 9 {i}^{2} \\ = 81 + 9 \\ = 90[/tex]