You can factor out across addition or subtraction, using the distributive property in reverse. For example, 8x^2 +4x=4x(2x+1)

Start by pulling out a common numerical factor from each of the terms. What factor do 15 and 5 share?

Next, look at each variable. How many times is x a factor of 15x^2 y^4 z^5? How many times is it a factor of -5x y^3 z^7 ? Factor out x as many times as you can — one (or sometimes both) terms will have no x left.

Then do the same for the other variables. If you’re still stuck, show us what you’ve got so far and we can suggest next steps. You can even post a picture of your work to imgur and drop the link.