The first step for solving this expression is to write -13xy as a difference.
x² - 4xy - 9xy + 36y²
Factor out x from the expression x² - 4xy.
x × (x - 4y) - 9xy + 36y²
Now factor out -9y from the expression -9y × (x - 4y)
x × (x - 4y) - 9y × (x - 4y)
Lastly,, factor out x - 4y from the expression to find your final answer.
(x - 4y) × (x - 9y)
Let me know if you have any further questions.
:)