Vector (A+B) will be perpendicular to?

I had this question in my coaching test. Shouldn't Vector (A+B) be perpendicular to A-B as A=B? As they form a rhombus and the diagonals of a rhombus are perpendicular to each other. I also drew it and am getting them to be perpendicular, for both A-B and 3A-3B. I checked the answer on Byju's and Toppr but it is also marked as A cross B there, so something must be wrong with my solution.