We were recently given a worksheet with some problems on it and I'm struggling with a few of the problems. Can anyone lead me in the direction or show me how to do some of these factoring problems?

Factor Fully.

1) 28s^2 - 8st - 20t^2

2) y^2 - (r - n)^2

3) 10x^2 + 38x + 20

4) y^5 - y^4 + y^3 - y^2 + y - 1

I'd greatly appreciate any help given for any of these problems. Thank you!