the question is; solve

z^2 + (2+4i)z -11 -2i = 0

well i did it and my answer is z= 6 + 2i and z= -6 -2i which i know is WRONG right?

BUT say if it is CORRECT, is that my final answer? or do i have to sub that in with something because i am sure you have to.

So can someone give me the correct answer and the steps involve as well as i want to crack this thing once and for all.