Answers: A, C, D
Explanation: Let (x-3)=0. x then equals 3. Substitute f(3) into each equation, and the ones which equal 0 are the answer.
As there is no any equation, I can't answer your question.
The amount of the substance (At) at any time t is calculated through the equation,
At = (A0)(e^-kt)
where A0 is the initial amount and k is constant.
For the half-life,
ln (At / A0) = ln 0.5 = -k(5270 years)
The value of k is 1.3153x10^-4 / year.
Substituting this value to the same equation, where At = 0.25A0
ln 0.25 = -(1.3153 x 10^-4)(t)
The value of t from this equation is 10540 years. The closest value to this is letter A.