For a particular isomer of $C_8{H}_{18},$ the combustion reaction produces $5113\mathrm{.}3kJ$ of heat per mole of $C_8{H}_{18}(g)$ consumed, under standard conditions.

$C_8{H}_{18}(g)+\frac{25}{2}{O}_2(g)--8C{O}_2(g)+9H_{2}O(g),H_{rxn}=-5113\mathrm{.}3k\frac{J}{m}ol$

What is the standard enthalpy of formation of this isomer of $C_8{H}_{18}(g)?$