The function c(x) = 600x – 0.3x2 represents total costs for a company to produce a product, where c is the total cost in dollars and x is the number of units sold.

This is what i got  hope i helped x=1996.66 repeated

3) we calculate the second derivative:
C´´(x)=-0.6;  because -0.6>0; we have a maximun at x=1000. 

4)We find out the maximum cost.

C(1000)=600(1000)-0.3(1000)²
C(1000)=600000-300000
C(1000)=300000
so the answer is (x)=-0.6; 

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