Please help me understand and guide me: Atomic Mass

Isotope ........................Atomic Mass (atomic mass units) ..........................Percent Natural Abundance

¹³⁰Xe....................................129.96............................................................................56.4%

¹³¹Xe ...................................^{130.94 .......................................................................................................36.9%}

¹³²Xe ....................................132.05............................................................................ 6.7%

Based on the atomic masses and the natural abundances shown in the data table, calculate the average atomic mass of calcium

2) the Table below gives information about two isotopes of element X

Isotope ........................................Mass...................................................... Relative Abundance

X-258 ............................................258.97 .......................................................82.41%

X-259 ............................................259.06 ........................................................17.59%

Calculate the average atomic mass of X

3) Naturally occurring isotopes of elemental antimony is a mixture of isotopes. the percent composition of the two most abundant isotopes is listed below:

-54.37% of the antimony atoms have a mass of 121 atomic mass units

-45.63 % of the antimony atoms have a mass of 122 atomic mass units

Calculate the atomic mass of antimony