Factors can be checked by reverse method, check the choices and find which prime matches the given:
Let us try the first item:
(x + 6y)(x-6y)
=x²-6xy +6xy -36y²
=x² - 0xy - 36y²
= x² - 36y²
Let us try the second item:
(x+6y)(x+6y)
=x² + 6xy +6xy + 36y²
=x² + 12xy + 36y²
Let us try the third item:
(x-6y)(x-6y)
=x²-6xy-6xy+36y²
=x² - 12xy +36y²
No correct factors from the given choices.
