My dad is horrible at math

I just figured this out now. And he's a pediatrician. He can't offer me anyhelp in this subject. I guess thats where my bad math skills came from. I have a test tommorow and I'M still not understanding FOIL or how to factor an expression such as 100b^2 + 180b + 81 into (10b+9)^2

or 4x^2 - 81y^2 into (2x+9y)(2x-9y)

Please and way of solving these problems into the easiest way is welcomed. I really hope I don't fail this math test but Im just not grasping this stuff im having an off week in math.