Which is equivalent to 16 Superscript three-fourths x?

RootIndex 4 StartRoot 16 EndRoot Superscript 3 x
RootIndex 4 x StartRoot 16 EndRoot cubed
RootIndex 3 StartRoot 16 EndRoot Superscript 4 x
RootIndex 3 x StartRoot 16 EndRoot Superscript 4