y=0.625x+1.75 is the equation for your problem.
Using formula a^2- b^2 = (a-b)(a+b)

It should be 3x^2y
I'm using 3 from numbers because 3 is a GCF of 18 and 15
Then I'm getting X^2 because it's the GCF of X^2 and X^3
Then I'm taking y because it's the GCF of y^3 and y
And finally we got no z on the left side so we get 3x^2y
It is going to be minus, so negative because a positive times by a negative always gives you negative.
i there would be two negative and three positive factors it would be a minus times by a minus which gives you a plus. if the amount of negatives is odd it will be negative, if it is even then it is going to end up being a positive.
hope i could help.:)