Find the cost per pound of a "house blend" of coffee that is made from 20 lb of central american coffee that costs $7 per pound and 30 lb of south american coffee that costs $4.50 per pound

Well first things first, you want to multiply 20 and 7, this way, you get $140 per lb. After this, you want to multiply 30 by 4.50, and you get $135 per lb. You want to add these two numbers, 140 + 135, and get the total sum of $275. And to find the per pound of this sum, the "house blend" you simply will need to add 7 and 4.50, to get $11.50 per pound. 

The correct answer will be d. -4