The summary formula for photosynthesis is #6CO_2 + 6H_2O → C_6H_12O_6 + 6O_2#. How many molecules of carbon dioxide would a plant have to use to produce three molecules of glucose?
We have the balanced chemical equation:
So, we see that six molecules of carbon dioxide produce one molecule of glucose, and that's the ratio between those two products and reactants.
So, if we want to produce three molecules of glucose, we would need: