(ab + b²)(a² + 6a) - (a² + ab)(b² + 6b) = ab(a + b)(a + 6) - ab(a + b)(b + 6) = ab(a + b)((a + 6) - (b + 6)) = ab(a + b)(a + 6 - b - 6) = ab(a + b)(a - b)
(ab + b²)(a² + 6a) - (a² + ab)(b² + 6b) = ab(a + b)(a + 6) - ab(a + b)(b + 6) = ab(a + b)((a + 6) - (b + 6)) = ab(a + b)(a + 6 - b - 6) = ab(a + b)(a - b)