When it comes to factoring you just look at what is common to parts of the expression, in this case 25 and 9 do not have any common factors, so there is no integer value to factor out, and the variables are all unique except that both parts of the expression have a "z" so

Now though, and this takes some insight, you may realize that is the difference of two perfect squares, and it is a well known fact that

So

and so the entire expression factors into