Need help on two proof questions I hope you guys can help!

There is alot on the internet but it's hard the way they explain it.

1) Prove that the centre of mass of a uniform wire in the form of a semi-circle of radiusris at a distance2r/pie(sorry don't know how to insert symbol) from the centre.

2) Prove that the centre of mass of a uniform semi-circular laminar of radiusris at a distance4r/3piefrom the centre.

Thanks