Question: how many moles are there in 24.0 grams of fef3?
Answer: 24 grams of FeF3 * (1 mole FeF3/ 112.8 gram FeF3) = 0.21 mole FeF3. That is it. In other words, there is 0.21 mole FeF3 in 24 grams of FeF3. I assume by this question that you are asking how many moles there are in 24g of FeF3.