1)Always write out the reaction first;
2NaCl+CaCo3-->Na2Co3+CaCl2
2)Now underneath calculate the Relative Formula Mass using a periodic table for each of the compounds.
CaCo3=100/ Na2Co3=106
3)Now always write out the formula you intend to use;
Moles= Mass of substance/ Relative formula mass
4)Always convert everything to grams so 20kg=20000g
Moles= 20 000/100
Moles= 200
5)Ratio of CaCo3 toNa2Co3 is 1:1 as seen in equation
so 200 moles= mass/ 106
therefore 200x106= mass
21200 mass in grams
or 21.2 kg