United Aluminum Company of Cincinnati produces three grades $($high$,$ medium, and low$)$ of aluminum at two mills. Each mill has a different production capacity $($in tons per day$)$ for each grade, as follows: The company has contracted with a manufacturing firm to supply at least $12$ tons of high$-$grade aluminum, $8$ tons of mediumgrade aluminum, and $5$ tons of low$-$grade aluminum. It costs United $\backslash (\backslash$$ $6000\backslash )$ per day to operate mill $1$ and $\backslash (\backslash$$ $7000\backslash )$ per day to operate mill $2.$ The company wants to know the number of days to operate each mill in order to meet the contract at the minimum cost. In the linear problem formulation, what is the high aluminium constraint?