Solve the Standard Minimization Problem Using Duality $c = 5 s + 4 t$

Short Answer

Solve the standard minimization problem using duality.
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Minimize $c = 5 s + 4 t$ ​
subject to $\begin{array} { l } 3 s + t \geq 30 \\s + t \geq 20 \\s + 3 t \geq 30 \\s \geq 0 , t \geq 0\end{array}$ ​ $c =$ __________
​ $s =$ __________
​ $t =$ ___________