Inverse radical change and percentage

Optional extension

The quantity \(y\) is inversely proportional to \(\sqrt{x-4}\), and \(y=\dfrac13\) when \(x=13\). Find

1. \(x\) when \(y=2\), and[2]
2. the percentage decrease in \(y\) when \(x\) rises from \(13\) to \(40\).[2]