Solve the following linear programming problem by applying the simplex method to the dual problem.

Minimize $C=2x_1+21x_2$

subject $to4x_1+x_{2}5$

$x_1+4x_{2}5$

$x_1,x_{2}0$

$C=2x_1+21x_2$

$4x_1+x_{2}5$

$x_1+4x_{2}5$

$x_1,x_{2}0$

Select the correct choice below and fill in any answer boxes present in your choice.

A$.$ MinC$=,$ at $x_1=,x_2=$

B$.$ There is no minimum value of $C$