Question 789015
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The solution and the answer in the post by @mananth are INCORRECT.


The correct solution is 


            V(x) = x*(20-2x)*(20-2x) = {{{x*(20-2x)^2}}} = {{{x*(400-80x+4x^2)}}} = {{{400x - 80x^2 + 4x^3}}}.