Δ = (8i)^2 - 4*(-25) => Δ = -36 +100 => Δ = 64 => x1 =(-8i + 8)/2 => x1 = -4i +4;
x2 = (-8i - 8)/2 => x2 = -4i-4; in this case, your solutions are complex conjugates.
Get them to have a common denominator so you can add them
(1/3)×2= 2/6 and (1/2)×3= 3/6
Add them together
(2/6)+ (3/6)= 5/6
So 5/6 of the class planted either marigolds or tulips and 1/6 of the class planted neither