Solve the Standard Minimization Problem Using Duality $c = 0.7 s + 0.3 t$

Multiple Choice

Solve the standard minimization problem using duality.
Minimize $c = 0.7 s + 0.3 t$
Subject to $$\begin{array} { l } 30 s + 20 t \geq 600 \\0.1 s + 0.4 t \geq 4 \\0.2 s + 0.3 t \geq 4.5 \\s \geq 0 . t \geq 0\end{array}$$

A) $c = 9 , s = 30 , t = 0$
B) $c = 21 , s = 0 , t = 30$
C) $c = 30 , s = 30 , t = 30$
D) $c = 9 , s = 0 , t = 30$
E) $c = 21 , s = 30 , t = 0$