7) How much tea costing $8 per pound should be mixed with 3 pounds of tea costing $5 per pound to get a mixture costing $6 per pound?

8) How many liters of water must evaporate from 40 liters of a 10% salt solution to make a 25% salt solution?

9) A candy shop has chocolate pieces that cost $2.50 per pound and caramel pieces that cost $1 per pound. How many pounds of each should be combined to get 20 pounds of a mixture worth $2 per pound?