Answer
b. F(B on H) = F (H on B) > F(A on B) = F (B on A)
Work Step by Step
The action-reaction pairs are F(B on H) = F (H on B) and F(A on B) = F (B on A). Since box B is slowing down, we know the is a net force in the opposite direction the boxes are moving. Newtons (f=ma) second law also tells us F(H on B) > F(A on B).
