Question 990242
Where is the derivative equal to zero?
Simplify that derivative and then solve this.


{{{yPrime=32x-1800/x}}}
{{{(32x)(x/x)-1800/x}}}
{{{(32x^2-1800)/x}}}
{{{(8/x)(4x^2-225)}}}


The factor of 8 can probably not be needed because you are looking for the NUMERATOR to be zero; and for the same reason, the x in the numerator is not important for this.
You now just need to solve for  {{{highlight_green(4x^2-225=0)}}}.