The power rule (or law of indices) that applies to this expression is
[tex] x^{ \frac{m}{n} } = \sqrt[n]{x^{m} } = ( \sqrt[n]{x}) ^{m} [/tex]
we have [tex]4 \sqrt{ y^{3} } [/tex]
we write [tex] \sqrt{ y^{3} } = y^{ \frac{3}{2} } [/tex] , note that square root [tex] \sqrt{x} [/tex] equals to [tex] \sqrt[2]{x} [/tex]
hence, the final expression is [tex]4( y^{ \frac{3}{2} } )[/tex]