we know that since we have an x^2 that somewhere we need an x times x
(?x ?)(?x ?)
We also have 1 xy term so we know we need an x times a y
(?x ?)(?x ?y)
We just need to find the coefficents that make it work. To get the 5y and the 5x we can really only have a 5 times a 1 because 5 is a prime number so we must have
(?x 5)(x y)
That also tells us that the first coefficent must be 6 becasue 6x times x is 6x^2 and 6x times y is 6xy. So we have
(6x 5)(x y)
Now we just need the proper signs. Positive 6x times postive x is 6x^2
positive 6x times -y is -6xy
-5 times x is -5x
-5 times -y is 5y
so your answer is
(6x-5)(x-y)