Mark M. answered 09/22/19
Retired math prof. Very extensive Precalculus tutoring experience.
m = a + bi and n = a - bi
So, (4+2i)(a+bi) - (1-i)(a-bi) = (4a + 4bi + 2ai - 2b) - (a -bi -ai -b) = (3a - b) + (3a + 5b)i = -9 + 9i
3a - b = -9 (real part = real part)
3a + 5b = 9 (imaginary part = imaginary part)
Subtract the equations to get -6b = -18
So, b = 3 and a = -2.
m = -2+3i and n = -2-3i.