Soybean meal is 18% protein, cornmeal is 19% protein.. how many pounds of each should be mixed in order to get 360lb mixture that is 17% protein?

S=weight of soybean protein, C=weight of cornmeal protein.
Total weight of each protein is 0.18S+0.19C=0.17×360=61.2 lb.
Total weight of meal is S+C=360 lb. So S=360-C.
Therefore 0.18(360-C)+0.19C=61.2, 64.8-0.18C+0.19C=61.2, 0.01C=-3.6.
Clearly we would get a negative value for C. When you look at the question you will realise that there is a larger percentage of protein in the ingredients than there is in the mixture. The expected amount of protein in the mixture should be between 18% and 19%. Please check your figures.

Provide an equation