The ideal gas constant, r has several different values that could be used. which quantity causes these differences

In my opinion, R in the ideal gas law claims a value of 0.08206 L*atm/(K*mol) and is a constant, which means its value would never change. 
Hope this helps~

Most likely a is the answer - because  you generate   38 atp's but also consume an atp.   each atp gives approx. less than 4 kcal so probably a is the closest answer.

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