Vector $\overrightarrow{\mathbf{A}}$ has a magnitude of 29 units and points in the positive $y$ direction. When vector $\overrightarrow{\mathbf{B}}$ is added to $\overrightarrow{\mathbf{A}},$ the resultant vector $\overrightarrow{\mathbf{A}}+\overrightarrow{\mathbf{B}}$ points in the negative $y$ direction with a magnitude of 14 units. Find the magnitude and direction of $\overrightarrow{\mathbf{B}}$ .