Hey there! I'm happy to help!
The Greatest Common Factor is self-explanatory: it is the largest factor that both numbers have in common. Let's look at the factors of each of these numbers:
30: 1, 30, 2, 15, 3, 10, 5, 6
45: 1, 45, 3, 15, 5, 9
We see that the largest number they both have in common is 15, so the GCF is 15.
Have a wonderful day! :D
