Question

The owner of a candy store want to sell, for $6 per lb, a mixture of chocolate-covered raisina, which usually sells for $3 per lb, and chocolate-covered macadamia nuts, which usually sells for $8 per lb. They have 40 lbs of raisins. How many lbs of the nuts should be mix with the raisins so that they hit their target value of $6 per lb mixture?