Chemistry Help ?

Question

 Calculate the average atomic mass for imaginary element “W” given the following information. There are 2 isotopes of this element, having atomic masses of
76.14 amu and 78.52 amu. The abundance of the first of these isotopes (Z-76) is 76.50 %.

Answer 1

abundance of first isotope (Z=76) = 0.7650

abundance of 2nd isotope = 1.000 - 0.0.7650 = 0.235

average atomic mass = (76.14)(0.76.50) + (78.52)(0.235) = 58.2471 + 18.4522 = 76.70