An element has three naturally occurring isotopes. the relative abundances of the isotopes are 0.27%, 9.25%, and 90.48%. the most abundant isotope has an atomic mass of 19.99 amu. the least abundant isotope has an atomic mass of 20.99 amu, and the remaining isotope has an atomic mass of 21.99 amu. based on these data, what is the average atomic mass of this element? (round your answer to the nearest hundredth and do not enter units in your answer.)