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Which of the following is equivalent to $ \sqrt { 6x } \cdot \sqrt [ 4 ]{ 9{ x }^{ 2 } } $?

$ 3x\sqrt { 6x } $

$ \sqrt { 15{ x }^{ 3 } } $

$ 3x\sqrt { 2 } $

$ \sqrt [ 4 ]{ 54{ x }^{ 3 } } $