Factorise completely:

16x - 4x + xy - 4y
= 4(4-x) + y(x-4)
= 4(x-4) + y(x-4)
=(x-4)(4+y)

Is this correct? I am not sure as the answer is (4-x)(4-y)

If I am wrong, can please show your workings? Thanks a lot!