There are a number of ways to do this. One way is to use a graphics program to measure it.
The angle is 71.6°.
Another way is to divide the vectors and look at the angle of the result. (8 +4i)/(9 -9i) = (8 +4i)(9 +9i)/162 = 36 +108i So the angle is arctan(108/36) ≈ 71.565° ≈ 71.6°
