we have
(6 - i) + (-7 +8i)
Combine like terms
(6-7)+(-i+8i)
-1+7i
we have
(6-i )+(-9+4i)
Combine like terms
(6-9)+(-i+4i)
-3+3i
we have
(3+4i )-(6-4i)
eliminate parenthesis
3+4i-6+4i
combine like terms
9i(5i)=45i^2
remember that
i^2=-1
so
45i^2=45(-1)=-45
