How many pounds of Brazilian coffee costing $ 6 per pound must be mixed with 27 lbs of Columbian coffee costing $ 4 per pound to produce a mixture costing $ 4.5 per pound.

11 2/3 pounds.

Step-by-step explanation:

Let x pounds be the amount in pounds of Brazilian coffee.

x + 27 is the amount of coffee in lbs after the mixing.

So, working in values of dollars, we have:

6x + 4*27 = 4.5 (x + 27)

6x + 104 = 4.5x + 121.5

1.5x = 121.5 - 104 = 17.5

x = 17.5/1.5 = 11 2/3 pounds answer