Line-height question

I have some questions about line-height…

1.) What does this do to line-height?

        body{
            font-size: 0.9em;
            line-height: 1.4;
        }

2.) What would this do in combination?

        body{
            font-size: 0.9em;
            line-height: 1.4;
        }

        a{
            line-height: 1.2;
         }

3.) Does “rem” work on line-height?