Explain a step for me !enter image description here Can someone please explain the high-lighted step to me? How does he get this result?

We have

$$(AB)^{-1}=B^{-1}A^{-1}$$ and of course we have a generalization: for example

$$(ABCD)^{-1}=D^{-1}C^{-1}B^{-1}A^{-1}$$