There is surely a typo in there somewhere as reading it gave me a headache :D
I believe it was intended to say that a pound of peanuts is $3.5 and a pound of covered peanuts is $2.75. Then we are to make a 12 pound mixture worth $3 a pound.
Let p be the pounds of peanuts and c be the pound of chocolate covered peanuts. Then:
(2.75p+3.5c)/12=3, given that p+c=12, c=12-p, making the equation become:
(2.75p+3.5(12-p)/12=3, multiply both sides by 12
2.75p+42-3.5p=36 combine like terms on left side
-0.75p+42=36 subtract 42 from both sides
-0.75p=-6 divide both sides by -0.75
p=8 lb, since c=12-p
c=4 lb
So the brothers should mix 8 pounds of regular peanuts with 4 pounds of chocolate covered peanuts to produce a 12 pound mixture worth $3 per pound.
