Answer:
1/4th the mass of Au-198
Explanation:
A half-life of 2.7 days means that in 2.7 days half of the Au-198 will be gone. This means that after 5.4 days, the amount of Au-198 will have undergone two half-life cycles resulting in there being 1/4th the amount of Au-198 left from the starting amount.
