How to get inner product of 3D array to 2D array?

Question

I have two Numpy array

b=np.array([[1, 2, 3], [4, 5, 6]])
a=np.array([[[1, 2,1], [3, 4,1],[4,5,6],[6,7,8]], [[5, 6,1], [7, 8,1],[4,5,6],[6,7,8]]])

a.shape,b.shap