Question 1128578
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{{{300/(r-15)-300/r=1&2/3}}},{{{5/3}}}

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{{{3r(r-15)(300/(r-15)-300/r)=3r(r-15)(5/3)}}}

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{{{180*15=r^2-15r}}}


{{{r^2-15r=2700}}}------------from here, if your instructions are to use Completing the Square, the term to use is  {{{(15/2)^2}}}, to add to both sides.
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(  answer:   r=60  )