Algebra
posted by Laura .
Soybean meal is 12% protein; cornmeal is 6% protein. howmany pounds of each should be mixed together to get a 240 pound mixture that is 8% protein?

Sum of protein constituents=total protein
.12S+.06P=240*(.08)
S + P=240
Those two equations will solve it. 
I don't understand the equations I am having a lot of trouble.

well, if
S+P=240, then S=240P
then
.12S+.06P=240*.08 or
.12(240P) + .06P=240*.08
solve for P