Question 883241
For a box, 
{{{V=L*W*H}}}
{{{V=x(10-x)(x/2)}}}
{{{V=(10-x)x^2/2}}}
{{{V=5x^2-x^3/2}}}
.
.
.
{{{SA=2LH+2LW+2WH}}}
{{{SA=2x(x/2)+2x(10-x)+2(10-x)x/2}}}
{{{SA=x^2+20-2x+10x-x^2/2}}}
{{{SA=30x-x^2}}}