Since you are dealing with hydrate compounds, this means that the water can be removed by itself until you're left with just the salt, so focus on balancing the salt equation and then add the water afterwards.
A). Na2CO3 → Na2O + CO2
now that we have the salt we can do the actual equation
Na2CO3•10H2O → Na2O + CO2 + 10H2O
B). MgSO4 → MgO + SO3
same concept as above
MgSO4•7H2O → MgO + SO3 + 7H2O