$-21 - 15i$
Work Step by Step
RECALL: (1) $a(b-c) = ac - bc$ (2) $i^2=-1$ Use rule (1) above to obtain: $=3i(7i) - 3i(5) \\=21i^2 - 15i$ Use rule (2) above to obtain: $=21(-1) - 15i \\=-21 - 15i$
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