You're already given the resultant in the question.
The triangle you draw should have 20 where the diagram says 'current vector', 27.5 where it says 'resultant vector', and the angle between the two should be 16 degrees. The 'second vector' is x.
You can use the cosine rule to find x (I make it 25.05N if you want to check) and then use the sine rule to get the obtuse angle between the 20N vector and vector x; then subtract this from 180 to get the correct angle.