Answer:
(a - 5)(a + 5 - b)
Step-by-step explanation:
given
a² - 25 - ab + 5b
a² - 25 is a difference of squares
= (a - 5)(a + 5) - ab + 5ab ← factor out - b from second/ third terms
= (a - 5)(a + 5) - b(a - 5) ← factor out (a - 5) from each term
= (a - 5)(a + 5 - b)