This is the concept of quadratic equations, solving the equation 2x^2-12x+20=0 using the formula we get:
x=[-b+/-sqrt(b^2-4ac)]/(2a)
from our equation, a=2,b=-12 and c=20
x=[-(-12+/-sqrt((-12)^2-4*2*20)]/(2*2)
x=[12+/-sqrt(144-160]/4
x=[12+/-sqrt(-16)]/4
x=[12+/-4i]/4
x=[3+\-i]
the answer is A] 3+/-i