So the equation is,
2Cl2(g) + 7O2(g) + 130kcal -> 2Cl2O7(g)
from this , ΔH°rxn=[tex]130kcal.mol^{-1}[/tex]
[tex]mol^{-1}[/tex] is mentioned because it is for per mole of reaction. So for 4. moles of the product [tex]2Cl_{2} O_{7}[/tex] we need 4/2 moles of reaction to be used to calculate associated enthalphy change for the reaction.
Therefore[tex]4/2*130=260 kcal[/tex]