Unfortunately, I cannot solve this problem with the information provided. The image shows a triangle ABC with points D on AC and M on BC. We are given angles: angle ABC = 40 degrees, angle BCD = 70 degrees, angle CDB = 40 degrees, and angle BDM = 40 degrees. We are also given CD = 14. However, the angles provided seem to lead to some isosceles triangles, but there isn't enough information to directly calculate the length of BM. It's possible there's a misunderstanding of the diagram or missing information.