Translation of "It´s" in Japanese

It´s all very well in theory, but will it work in practice?

理論は結果だが実際にうまくいくだろうか。

It´s an excellent piece of work. You´ve certainly been polishing your skills, haven´t you!

なかなかの出来だ。君もずいぶん腕を磨いたじゃないか。