An element E has three isotopes:
\(28\\14 E\) (abundance 92.21%, atomic mass: 27.977 a.m.u.),
\(29\\14 E\) (abundance 4.70%, atomic mass: 28.976 a.m.u.), and
\(30\\14 E\) (abundance 3.09%, atomic mass: 29.974 a.m.u).
The atomic mass of E is _______ a.m.u.
(rounded off to three decimal places