Agnes has 23 collectible stones, all of which are labradorite crystals or galena crystals.
Labradorite crystals are worth $20 each, while
galena crystals are worth $13 each. Agnes
earns $439 by selling her entire collection. How
many stones of each type did she sell?

Your vet has placed your pet on a diet. the diet is to contain at least 12 mg of fat and at least 14 mg of protein per serving. these requirements are to be obtained from two food sources. source a contains 2 mg of fat and 2 mg of protein per serving. source b contains 1 mg of fat and 3 mg of protein per serving. if source a sells for $1.28 per serving and source b sells for $1.12 per serving, how many servings of each type should be purchased to satisfy the requirements at minimal cost?