Maximize $z=x_1+2x_2+4x_3+6x_4$

subject $to$: $x_1+2x_2+3x_3+x_{4}100$

$3x_1+x_2+2x_3+x_{4}75$

with $x_{1}0,x_{2}0,x_{3}0,x_{4}0$

A$.$ Maximum is $150$ when $x_1=0,x_2=75,x_3=0,x_4=0$

B$.$ Maximum is $450$ when $x_1=0,x_2=0,x_3=0,x_4=75$

C$.$ Maximum is $300$ when $x_1=0,x_2=0,x_3=75,x_4=0$

D$.$ Maximum is $600$ when $x_1=0,x_2=0,x_3=0,x_4=100$