Hello! I am in Calc III, and I have a question. The answer sheet gives me a different answer than I have, but I feel that I am correct. Could you all point me one way or another?

Parallelogram with points: A(2, -1, 4); B(1,0,-1); C(1,2,3); D(2,1,8)

The question is.... what is the interior angle at B?

The answer sheet says use vectors AB and BC and comes up with 140.8 degrees.

I used vectors BA and BC and got 39.23 degrees.

Which one is correct? Thanks!