Calculate the time it will take for the amount of Niobium-92 to reach 25.0% of its initial amount. The half-life of Nb-92 is 34.7 million years.

• A. 1.44×10⁷ years
• B. 3.27×10⁷ years
• C. 6.94×10⁷ years
• D. 5.50×10⁷ years

Answer: (C)