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**rhhs11** ok, so i differentiated and i got $\displaystyle x=600/(3+(3)^(0.5)$ which equals 126.8. So i subbed that into total Area equation which is $\displaystyle A=300x - 3x^2 + x^2(3)^(0.5)/x$.

I get $\displaystyle A(126.8) = 20884.7cm$ but the answer is $\displaystyle 2.1 m^2$ (Worried)

$\displaystyle 600=3x+2y$...so $\displaystyle y=\frac{-3(x-200)}{2}$...imputting that into your area equation you get $\displaystyle A=x\cdot\bigg(\frac{-3(x-200)}{2}\bigg)$..differentiating we get $\displaystyle A'=300-3x$ which equals zero at x is equal to 100...now to check if its a max we find the second derivative $\displaystyle A''=-3$...which is always negative...therefore $\displaystyle x=100$ is a max...substitute it into your perimeter equation and get x