Final answer:
After 36.9 years, using the half-life of 12.3 years for hydrogen-3, you would be left with 1/8 or 12.5% of the original amount.
Step-by-step explanation:
The fraction of hydrogen-3 that would be left after 36.9 years can be calculated using its half-life, which is 12.3 years. After one half-life (12.3 years), you would have half of the original amount of hydrogen-3. After two half-lives (24.6 years), you would have a quarter, and after three half-lives (36.9 years), you would be left with an eighth of the original amount. So, after 36.9 years, 1/8 or 0.125 (12.5%) of the original hydrogen-3 would remain.