8i is completely imaginary, so it would be vertical. It's positive, so it would be directly up. The angle of that would be π/2. The magnitude would be 8.
Going the long way though, the angle can be obtained by arctan(o/a), where o is the height (imaginary part) and a is the adjacent, real part.
arctan(8/0)
As tangent is sine/cosine, when cosine is 0, tangent is undefined and the angle is:
= ±π/2
The imaginary part is positive, so π/2 is chosen.
The magnitude is given by the Pythagorean theorem applied to the real and imaginary