Hot dog mixture in 1000-pound batches. Two ingredients, chicken ($3/lb.) and beef ($5/lb.). Recipe requirements: at least 500 pounds of chicken and at least 200 pounds of beef. The ratio of chicken to beef must be at least 2 to 1. The optimal mixture of ingredients that will minimize costs is:  a- x1=2, x2=4 and min. cost =28 b- x1=0, x2=5 and min. cost =25 c- x1=4, x2=2 and min. cost =26 d-x1=4, x2=0 and min. cost =16