Factoring f(x) would give a factor (x-1-2i), so you can divide f(x) by this, leaving (x-3)(x+4)(x-1+2i), so the other roots are:
x=3
x=-4
x=1-2i
Are you asking to find the difference?
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Answer:
C gives you 90.2
Step-by-step explanation:
84+88+90+100=362
362/4=90.2