Final answer:
The average atomic mass of element X can be calculated by multiplying the mass of each isotope by its abundance and summing the results.
Step-by-step explanation:
The average atomic mass of an element can be calculated by multiplying the mass of each isotope by its abundance and summing the results. In this case, element X has two naturally occurring isotopes: 90X with an abundance of 75% and a mass of X amu, and 94X with an abundance of 25% and a mass of Y amu. To calculate the average atomic mass, we can use the following equation:
Average Atomic Mass = (Abundance of 90X * Mass of 90X) + (Abundance of 94X * Mass of 94X)
By substituting the given values for abundances and masses, we can calculate the average atomic mass of element X.