A 26.9 g gram sample of impure potassium nitrate (KNO3) was heated to complete decomposition according to the equation:
2KNO3(s) --> 2KNO2(s) + O2(g)
After the reaction was complete, the solid residue, consisting of KNO2 and the original impurities, had a mass of 24.1 g. Assuming that only the potassium nitrate had decomposed, how many grams of KNO3 were present in the original sample? Answer in units of g.