(n_out, n_in) - **a**^[l-1] has shape **(64, 16)** --- (n_in, batch_size) - **b**^[l] has shape **(32, 1)** --- (n_out, 1), broadcast across the 16 columns - **z**^[l] has shape **(32, 16)** --- (n_out, batch_size)