Question 1199169
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{{{ y = k*(1/x^3) }}}
{{{ x[2] = (3/4)x }}}  <<< {{{x[2]}}} is 75% (=100%-25%) of x
{{{ y[2] = k(1/(x[2])^3) }}} 
{{{ y[2] = k(1/((3/4)x)^3)  = k(1/((27/64)x^3) ) = (64/27)*k*(1/x^3) }}}

Substitute y for {{{k(1/x^3) }}} 

{{{ y[2] = (64/27)y }}}  or approx. {{{ y[2] = 2.37y }}}

Percentage change in y:  {{{ (y[2]-y)/y * 100 = (2.37y - y)/y * 100 }}} = 137%