If the expression is 8x^3y - 24x^2y^9 + 16xy^8
There are three parts: one before the minus sign, one after the plus sign and one in the middle.
They have common terms that can be removed and placed in parentheses in front to multiply it with what's left.
Your three "x" terms are x cubed, x squared and x so, the largest x term that goes into each is x.
Your three "y" terms are y, y to the ninth and y to the eighth power so the largest y term that goes into each is y.
Your three coefficients are 8, 24 and 16 so that largest number that you can divide into them is 8
So you can take out 8xy and rewrite the expression as: 8xy(x^2 - 3xy^8 + 2y^7)
Multiply it and see if it works. . . Remember that you add exponents when you multiply numbers.