A two$-$component model used to determine percent body fat in a human body assumes that a fraction ff $(<1<1)$ of the body's total mass mm is composed of fat with a density of $0\mathrm{.}90$ g$/$cm$3$g$/$cm$3,$ and that the remaining mass of the body is composed of fat$-$free tissue with a density of $1\mathrm{.}10$ g$/$cm$3$g$/$cm$3.$

If the specific gravity of the entire body's density is XX$,$ find the percent body fat $(=$f$100=$f$100).$

Express your answer in terms of XX$.$