The element uranium ( U ) has three naturally occuring isotopes, U234 , U235 , and U238 . U234 has an isotopic mass of 234.04 u and a relative abundance of 0.0054%. U235 has an isotopic mass of 235.04 u and a relative abundance of 0.7204%. U238 has an isotopic mass of 238.051 u and a relative abundance of 99.2742%. Calculate the average atomic mass of uranium.