Long division of polynomials is the same as that of integers.
We find the number that we can multiply (4x + 5y) by to obtain the given polynomial. This is (4x - 5y).
Moreover, this is visible from the fact that
(16x² - 25y²) satisfies the identity:
(a² - b²) = (a + b)(a - b); where a = 4x and b = 5y
