Incorrect Answer.
p is false at world d, so K1p and K3p are both false at d, and hence E{1,3}p is false at d. Since worlds a, c and d are all 1-related to each other, K1p is false at all of them, and so E{1,3}p is aslo false at a, c and d. Worlds a, b and d are all 3-related to each other, so K3p is false at all of them, and so E{1,3}p is also false at a, b and d. Therfore E{1,3} is false at all the worlds a, b, c and d.
Back to Question.
Next Question.