Let x = amount of soy meal to be mixed. 16% of this amount is protein, or 0.16x.

Let y = amount of corn meal to be mixed. 8% of this amount is protein, or 0.08y.

The total mixture is 320 lb. The first equation represents the amounts mixed overall:

The total mixture is 15% protein, or 0.15(320) = 48. The second equation represents the amount of protein:

So here we have a system of equations:

Solve for x and y.

EDIT: Typos.