First look at the molar mass of Al, which is 26.98 grams. That means that there are 26.98 grams in one mole of Al. To find the moles in your given sample of 64.1 grams, just divide that value by the molar mass of 26.98 grams. That will give you a final answer of 2.38 moles in 64.1 grams of Al.
Hope this helps!
