30x^4yz^3 = 2 * 3 * 5 * x * x * x * x * y * z * z * z
75x^4z^2 = 3 * 5 * 5 * x * x * x * x * z * z
The greatest common factor (GCF) is made of the parts that appear in both 30x^4yz^3 and 75x^4z^2. In this case that list is 3 * 5 * x * x * x * x * z * z because those parts appear in both 30x^4yz^3 and 75x^4z^2.
3 * 5 * x * x * x * x * z * z = 15x^4z^2
Answer: 15x^4z^2