50 ! soybean meal is 16% protein; cornmeal is 8% protein. how many pounds of each should be mixed together in order to get 320-lb mixture that is 9% protein? how many pounds of cornmeal should be in the mixture? how many pounds of soybean should be in the mixture?

The first thing we are going to do for this case is define variables.
 We have then:
 x: Amount of soybean meal
 320 - x: quantity of cornmeal
 We now write the equation that models the problem:
 
 Rewriting we have:
 
 From here, we clear x:
 
 Then, the amount of Soybean meal is:
 
 The amount of cornmeal is:
 
 
 cornmeal: 280 lb
 Soybean: 40 lb.