Assume BC is the diameter of the Ferris wheel centre O. AOB is an isosceles triangle where AO=BO (radii). So angles ABO and BAO are equal. They must add up to 180-120=60, so each must be 30 degrees. ABO=30 degrees. The diameter of the wheel and the position of point E are not relevant in this solution. I guess there are other parts to the question where they would be important.