CLAIM: The material is approximately 105 months (8.75 years) old.
EVIDENCE: The material contains 6.25% of the original radioactive atoms.
REASONING: We can use the formula for radioactive decay to calculate the age of the material. The formula is:

where N is the final amount of radioactive atoms, N0 is the initial amount of radioactive atoms, t is the time that has passed, and T is the half-life of the material.
We know that N = 0.0625 N0, since only 6.25% of the original radioactive atoms are present. We also know that T = 35 months, the given half-life. Substituting these values into the formula, we get:
)
Dividing both sides by N0, we get:

Taking the logarithm of both sides, we get:

Solving for t, we get:

Using a calculator, we can evaluate the right-hand side of this equation to be approximately 105 months (8.75 years).
CONCLUSION: The material is approximately 105 months (8.75 years) old based on the evidence and reasoning presented above.