Step #1: Convert to grams.
120kg × (1000g ÷ 1kg) = 120000g of copper
Step #2: Convert sample mass of copper to moles by dividing sample mass to its atomic weight. Atomic weights could be found in periodic table.
120000g Cu × (1mol Cu ÷ 63.55g Cu) = 1888.277mol Cu
Step #3: Convert moles to atoms by multiplying moles to Avogadro's number.
1888.277mol Cu × (6.022x10^23 ÷ 1mol Cu) = 1.137x10^27 atoms Cu
*I attached a picture to help out with conversions.
