Question

Calculate the number of moles of calcium chloride that can be obtained in 30g of calcium trioxocarbonate (vi) in the presence of excess hydrochloric acid

Answer 1

Where did you get the name of calcium trioxocarbonate (vi)? There is no such compound. You may have meant CaCO3 which is properly called calcium carbonate.
CaCO3 + 2HCl ==> CaCl2 + H2O + CO2
mols CaCO3 = g/molar mass = about 30/100 = 0.30
So you can 0.30 mols CaCl2 from 0.30 mols CaCO3.