Which expression is equivalent to RootIndex 4 StartRoot 144 a Superscript 12 Baseline b cubed EndRoot? Assume a greater-than-or-equal-to 0 and b greater-than-or-equal-to 0. 2 a cubed (RootIndex 4 StartRoot 9 b cubed EndRoot) 2 a Superscript 4 Baseline b (RootIndex 4 StartRoot 18 EndRoot) 6 a cubed (RootIndex 4 StartRoot 3 b cubed EndRoot) 12 a Superscript 6 Baseline b (RootIndex 4 StartRoot b EndRoot)