You follow the rules for the quadratic formula, where
x= (-b +- √(b²-4ac) )/2a
Filling a, b and c in yields
x = (8 +- √(64-164) ) / 2 =>
x = (8 - √-100)/2 or x = (4 + √-100)/2
Well, √-100 = 10i, so then you simplify to the last answer, D:
x = 4-5i or x=4+5i