Answer
Atomic mass of Iron = $55.8473amu$
Work Step by Step
Mass of $^{54}Fe = 53.9396 amu $
% abundance = $5.82\%$
Mass of $^{56}Fe = 55.9349amu$
% abundance = $91.66\%$
Mass of $^{57}Fe = 56.9354amu$
% abundance = $2.19\%$
Mass of $^{58}Fe = 57.9333amu$
% abundance = $0.33\%$
Atomic mass of an element is the weighted average of the constituent isotopes.
I.e., atomic mass of Iron =
$0.0582(53.9396amu)+0.9166(55.9349amu)+0.0219(56.9354amu)+0.0033(57.9333amu)$
Atomic mass of Iron = $55.8473amu$
