Hey Nicole! So you just need to multiply the number of moles with the molar mass of the molecule.
First compute for the molar mass, you can get the atomic mass of each element from the periodic table. Also, the subscript for each molecule means you will have to multiply the atomic mass by that number:
AM Na = 22.99 g/mol AM C = 12.01 g/mol AM O =16.00 g/mol
MM Na2CO3 = 2(AM Na)+(AM C) + 3(AM O) = 2(22.99 ) + 12.01 + 3(16.00) = 105.99 g/mol
Now Get the mass
mass Na2CO3 = (moles Na2CO3)(MM Na2CO3) = (0.719 mol)(105.99 g/mol)
= 76.207 g