${\mathrm{Fe}}_2{\mathrm{O}}_{3\left(\mathrm{g}\right)}+3{\mathrm{CO}}_{\left(\mathrm{g}\right)}\to 2{\mathrm{Fe}}_{\left(\mathrm{s}\right)}+3{\mathrm{CO}}_{2\left(\mathrm{g}\right)};\mathrm{\Delta H}=-26.8\mathrm{kJ}$
${\mathrm{FeO}}_{\left(\mathrm{g}\right)}+{\mathrm{CO}}_{\left(\mathrm{g}\right)}\to {\mathrm{Fe}}_{\left(\mathrm{s}\right)}+{\mathrm{CO}}_{2\left(\mathrm{g}\right)};\mathrm{\Delta H}=-16.5\mathrm{kJ}$
From the above data, 
The value of $\mathrm{\Delta H}$ for the following reaction ${\mathrm{Fe}}_2{{\mathrm{O}}_3}_{\left(\mathrm{g}\right)}+{\mathrm{CO}}_{\left(\mathrm{g}\right)}\to 2{\mathrm{FeO}}_{\left(\mathrm{s}\right)}+{\mathrm{CO}}_{2\left(\mathrm{g}\right)}$ is

${\mathrm{Fe}}_2{\mathrm{O}}_{3\left(\mathrm{g}\right)}+3{\mathrm{CO}}_{\left(\mathrm{g}\right)}\to 2{\mathrm{Fe}}_{\left(\mathrm{s}\right)}+3{\mathrm{CO}}_{2\left(\mathrm{g}\right)}$
$\mathrm{\Delta H}=-26.8\mathrm{kJ}.......\left(\mathrm{i}\right)$
${\mathrm{FeO}}_{\left(\mathrm{s}\right)}+{\mathrm{CO}}_{\left(\mathrm{g}\right)}\to {\mathrm{Fe}}_{\left(\mathrm{s}\right)}+{\mathrm{CO}}_{2\left(\mathrm{g}\right)}$
$\mathrm{\Delta H}=-16.5\mathrm{kJ}.....\left(\mathrm{ii}\right)$
${\mathrm{Fe}}_2{\mathrm{O}}_{3\left(\mathrm{g}\right)}+{\mathrm{CO}}_{\left(\mathrm{g}\right)}\to 2{\mathrm{FeO}}_{\left(\mathrm{g}\right)}+{\mathrm{CO}}_{2\left(\mathrm{g}\right)}$
$\mathrm{\Delta H}=?.....\left(\mathrm{iii}\right)$
Eq. (iii) can be obtained as : 
(i)-  2(ii) = -26.8 – 2(-16.5) = - 26.8 + 33.0 = + 6.2 kJ