Question reg Operation of Linear lagebra

Hi,

I have doubt regarding Logic on how it is able to performed this .
array_a = np.array([[7,8,9]])
array_a
Shape 1*3

array_b= np.array([[1,2,3],[4,5,6]])
array_b

shape 2*3

Can you please explain how it is able to perform Matrix sum and multiplication  with 1*3 and 2*3 shape .I thought  m*n and n*p only when these conditions are satisfied, then only operations are possible
As I can see operation is happening here so just wanted to understand in bit more detail mathematically.

Regards,
Manas