I can't answer the first and the last question because no given data is provided. However, I can answer the second question.
if 1/8 of a radioactive element remains after 600 years, what is that element's half-life?
The formula for half life, t1/2, is:
t1/2 = ln2/K
So we must determine K first. The formula for that is:
A = A₀e^(-kt)
where
A = 1/8*A₀
t = 600 years
Thus,
1/8*A₀ = A₀e^(-k*600)
1/8 = e^(-600k)
Solving for k,
K = 3.466×10⁻³
Therefore,
t1/2 = ln2/3.466×10⁻³ = 200 years