(х-3)^2-(4+х)(х-4) = (х-3)(х-3) - (4+х)(х-4)
= x^2 - 6x + 9 - (4x - 16 + x^2 - 4x)
= x^2 - 6x + 9 - 4x + 16 - x^2 + 4x
= -6x + 9 + 16
= -6x + 25

Ответ: -6x + 25.