A mixture of FeO and $Fe_3O_4$ when heated in air to a constant weight,gains 5% of its weight,Find the composition of the initial mixture.

Question

$(a)\;21.5\%,78.5\%\qquad(b)\;22\%,78\%\qquad(c)\;20.25\%,79.75\%\qquad(d)\;20\%,80\%$