How many moles of ATP must be converted to ADP by the reaction

ATP(aq) + H2O ---> ADP(aq) + HPO4-2(aq) + 2H+(aq) delta-G*= -31 kJ

to bring about a nonspontaneous biochemical reaction in which delta-G*= +372 kJ?

I did my work out like this..:
372 kJ x 1 mol/-31 kJ = -12 mol
But how can I get negative moles?? Is there a different way to do this problem?

You cant get an endothermic reaction from a exothermic reaction. Your basic reaction is exothermic. You are trying to get a +G, endothermic. Not possible. If you try the math,you get negative matter (neg moles).

So as an answer would I just say that it's not possible?