Hey there!
Find the molar mass of Na₂CO₃.
Na: 2 x 22.99 = 45.98
C: 1 x 12.01 = 12.01
O: 3 x 16 = 48
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105.99 g/mol
We have 0.750 mols of Na₂CO₃.
105.99 x 0.750 = 79.5
0.750 mols of Na₂CO₃ is 79.5 grams.
Hope this helps!