Consider the following cases of standard enthalpy of reaction $\left({\mathrm{\Delta H}}_{\mathrm{r}}^{\circ }\text{ in }{\mathrm{kJmol}}^{-1}\right)$

$\begin{array}{l}{\mathrm{C}}_2{\mathrm{H}}_6\left(\mathrm{g}\right)+\frac{7}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2{\mathrm{CO}}_2\left(\mathrm{g}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\ell \right){\mathrm{\Delta H}}_1^{\mathrm{o}}=-1550\\ \mathrm{C}\left(\text{ graphite }\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{CO}}_2\left(\mathrm{g}\right){\mathrm{\Delta H}}_2^{\mathrm{o}}=-393.5\\ {\mathrm{H}}_2\left(\mathrm{g}\right)+\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{H}}_2\mathrm{O}\left(\ell \right){\mathrm{\Delta H}}_3^{\mathrm{o}}=-286\end{array}$

The magnitude of ${\mathrm{\Delta H}}_{f C_2{\mathrm{H}}_6\left(\mathrm{g}\right)}^{\mathrm{o}}$ is ______ kJ mol^–1 (Nearest integer).