How would you balance: Na2CO3 + H2PO4 --> H2O + CO2 + Na3PO4?
Balancing a chemical equations is either done by coefficients or exponants.
For this particular reaction, the amount of Na on both sides needs to be balance. Therefore, I balance it out through
3Na2CO3 + H2PO4 --> H2O + CO2 + 2Na3PO4
Lastly, check to see if all other atoms are balanced.
To note, for this topic, practice makes perfect.