Question 623479
{{{ (4x/y^3)^-3 }}}
the reciprocal gets rid of the neg exponent
{{{ (y^3/4x)^3 }}} = {{{ (y^9)/(4^3x^3) }}} = {{{ y^9/(64x^3) }}}
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I think you are making this harder than it is,
 remember you have to raise 4 to the third power also, but it looks like you know what you are doing