How do you find the GCF of each?

The first step is to consider the GCF of the numbers (coefficients) separately from that of the x’s and that separately from the GCF of the y’s.

For the coefficients, take the smaller number (so 30 in the exercise #12) and find all the numbers that divide into 30:
1, 2, 3, 5, 6, 10, 15, 30
Then start with the largest of those and see which is the first to divide into 66.
30 does not divide evenly into 66.
15 does not divide evenly into 66.
10 does not divide evenly into 66.
6 does. You’ll use 6.

For the x’s, consider how many x’s each expression has.
66yx has 1 x
30x^2y has 2 x’s.
The greatest number they all have is 1 x.

For the y’s, do the same thing:
66xy has 1 y.
30x^2y has 1 y.
They both have 1 y in common.

So the greatest things they all have in common are 6xy. That’s your GCF.