So to find the Greatest Common factor we need to list the factors of 30 and 45.
30: 1,2,3,5,6,15,30
45: 1,3,5,9,15,45
As you can see the greatest factor of BOTH of them is 15 so The Greatest Common Factor of 30 and 45 is 15! Hope I helped you with your question! Have a great day! =)