Answer:
$6 per lb.
Explanation:
Given :
1 lb of blend -----> costs $7
Assume that we make 3 lbs of blend :
3 lbs of blend -----> costs $7 x 3 = $21
we are also given that blend is made from a ration of 2: 1 of arabica: robusta,
hence 3 lb of blend will be made out of 2 lbs of arabica and 1 lb of robusta.
Considering the costs:
Cost of 3 lb of blend = cost of 2 lb of arabica + cost of 1lb of robusta
we are given that robusta is $9 for 1 lb,
hence substituting what we know into this equation
$21 = cost of 2 lb of arabica + $9
cost of 2 lb of arabica = $21 - 9 = $12
cost of 1 lb of arabica = $12 / 2 = $6 per lb.