Answer:
35.4575 amu
Explanation:
We use the relative abundance of each of the isotopes.
Let the isotopes be A and B.
Since A is having an abundance of 75.53, the abundance of B would be 100 - 75.53 = 24.47%
The average atomic mass is calculated as follows;
(75.53/100 * 34.96885) + (24.47/100 * 36.96590) = 26.4119 + 9.0456 = 35.4575 amu