Final answer:
The half-life of the substance is approximately 307.13 days.
Step-by-step explanation:
The half-life of a radioactive substance can be determined by finding the time it takes for the amount of the substance to decrease to half its original value.
In this case, the substance decayed to 79.6% of its original amount after 300 days.
To find the half-life, we can use the formula:
Half-life = (Time elapsed × ln(2)) / (ln(Initial amount) - ln(Final amount))
Half-life = (300 days × ln(2)) / (ln(1) - ln(0.796))
After calculating this expression, we find that the half-life of the substance is approximately 307.13 days.