What is the current optimal solution and the objective function value?

$6000(1\mathrm{.}25)+7000(0\mathrm{.}5)=9750$

What is the objective function coefficient of decision variable $1($operation days of mill $1)?$

What is the sensitivity range for the objective function coefficient of decision variable $1($operation days of mill $1)?$

If the operation cost of mill $1$ increases from $$6000$ to $$7500,$ will the optimal solution change? And why?

What is the objective function coefficient of decision variable $2($operation days of mill $2)?$

What is the sensitivity range for the objective function coefficient of decision variable $2($operation days of mill $2)?$

If the operation cost of mill $2$ decreases from $$7000$ to $$6500,$ will the optimal solution change? And why?

Which constrains are binding?

If we can decrease the demand of high$-$grade aluminum by $2$ tons at the cost of $$\frac{1000}{?}$ ton, is it worth doing this? A

If the demand of medium$-$grade aluminum increases by $4$ tons, what is the new total cost? And why?