The assimilatory power needed to fix six ${\mathrm{CO}}_2$ molecules in a ${\mathrm{C}}_3$ plants during dark reaction of photosynthesis is

In one turn of the Calvin cycle, one CO₂ molecule is fixed utilizing 3 ATP and 2 NADPH molecules. Therefore, in order to fix 6 CO₂ molecules, 18 ATP and 12 NADPH molecules are required.