The balanced equation of photosynthesis is: 6CO2 + 6H2O + light energy = C6H12O6 + 6O2.
The correct answer is that "it is equal to the total mass of carbon dioxide and water used" as the substrates (CO2 and H2O) are just merely converted to the products (C6H12O6 and O2) with no mass being consumed or used as fuel for the reaction. In this reaction, energy is well conserved.