The Standard Free-Energy Changes for the Reactions Below Are Given

The standard free-energy changes for the reactions below are given.
Phosphocreatine → creatine + P_i
ΔG^0' = −43.0 kJ/mol
ATP → ADP + P_i
ΔG^0' = −30.5 kJ/mol
What is the overall DG0′ for the following reaction?
Phosphocreatine + ADP → creatine + ATP

A) −73.5 kJ/mol
B) −12.5 kJ/mol
C) +12.5 kJ/mol
D) +73.5 kJ/mol
E) ΔG^0' cannot be calculated without Keq'