3 questions. please help

An element has two naturally occurring isotopes. Isotope 1 has a mass of 120.9038amu and a relative abundance of 57.4%. Isotope 2 has a mass of 122.9042amu. Find the atomic mass of this element and then identify it. The foul odor of rancid butter is due largely to butyric acid, a compound containing carbon, hydrogen, and oxygen. Combustion analysis of a 4.30g sample of butyric acid produces 8.59gCO2 and 3.52g H2O. Determine the empirical formula of butvric acic A chemist decomposed a compound and found it contained 1.443gSe and 5.841gBr. Determine th empirical formula of the compound