Here are the questions:
an expression is shown below:

2x3y + 8xy − 4x2y − 16y

part a: rewrite the expression so that the gcf is factored completely. (4 points)

part b: rewrite the expression completely factored. show the steps of your work. (6 points)

now, here's my problem:

my
part a: ↓
gcf of coefficients: ↓
coefficients: 2, 8, -4, -16
factors of 2: 1, 2
factors of 8: 1, 2, 4, 8
factors of -4: -1, 4, 1, -4, -2, 2
factors of -16: -16, 1, 16, -1, -4, 4, -2, 8, 2, -8
common factors: 1, 2
gcf: 2
gcf of variables: ↓
variables: x^3y, xy, x^2y, y,
factors of x^3y: x^3, y, x, 3
factors of xy: x, y
factors of x^2y: x^2, y, x, 2
factors of y: y
common factors: ? ?

don't i need a gcf for both x and y? is it prime, or is it only y as the gcf of the variables? me !