Question

add the following thermochemical equations:
(1) P4(s) + 6Cl2(g) => 4PCl3(g) chg of H= -1148kJ
(2) 4PCl3(g)+4Cl2(g) =>4PCl5(g) chg of H=-460kJ
(3) overall equation= ? chg of H overall= ?
Select the correct chg of H for the overall process (equation 3)
A. -688 kJ
B. 688 kJ
C. -1608 kJ
D. 1608
E. none of these

i don't even really understand the question, any help? this is my first time using open study...