In your case, there are two possibilities: x-3=y or x/2=y. In the first case, y=7. In the second case, y=5. Make sure you address this problem with your teacher.
x6 - y6 = (x3)2 - (y3)2 = (x3 + y3) (x3 - y3) = (x + y)(x2 - xy + y2)(x - y)(x2 + xy + y2)
6y-y3 = 3
x3-y3
-y3 + 7y3
72
27-y3 factored completely = 24
X2+Y3+15 All you can do is simplify it.
No
12x2 - 24x + 9y
30
y times y times y (or y3)
The GCF of y3, y7, y8 is y3