How do we write the MIMO state space representation of the model? For example given the below MIMO ARX model:

y1(k) = -a1*y1(k-1) - a2*y2(k-1) + b1*u1(k-1) + b2*u2(k-1) + b3*u1(k-2) + b4*u2(k-2)

y2(k) = -a3*y1(k-1) - a4*y2(k-1) + b5*u1(k-1) + b6*u2(k-1) + b7*u1(k-2) + b8*u2(k-2)

How do we write them in state space representation? This is a 2 inputs 2 outputs system. Thanks.