Astudent sets up two reactions. reaction 1 uses 0.170 mol/l of reactant, and reaction 2 uses 0.400 mol/l of reactant. how many times faster is reaction 2 compared to reaction 1?

In chemical reaction dynamics, the rate of the reaction can take different forms depending on the type. If we are to take this reaction as a first-rate reaction then, the rate is dependent to the concentration of the reactant.
                                n = 0.400 molL  / 0.170 mol/L
                                 n = 2.35 times
Thus, the second rate is 2.35 times the 1st rate. 

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.