I said the vertex of the angle at the center of the protracter, and then, what you wanna do is, either rotate the angle or rotate the protractor in this case you are going to rotate the protractor you wanna rotate the protracor so that the zero angle are look at the zero mark is at one of the sides of the angle and the other side of the angle is within the protractor so lets,try to do that so if may be ,if you wanna do that this zero side it should be at this side of the angle so lets,rotate it