In order to know the number of moles from the given mass, the conversion factor to be used is the average atomic mass of Calcium which is equal to 40.08 g/mol. But first, let's convert mass from grams to kilograms knowing that there are 1,000 g in every 1 kg.
Mass = 351 kg * 1,000g/1 kg = 351,000 grams
Number of moles = 351,000 g * 1 mol/40.08 g = 8,757.5 moles Calcium