Two blocks, A and B, are stacked. Block B is attached to a wall by an inextensible string. A force of 25 lb is applied to Block B, which is enough to make it slide to the left. If $$mu_k=0.4$$ between A and B, and if $$mu_k=0.6$$ between B and the floor, the acceleration of B $$(ft//s^2)$$ is most nearly:
