The half life for the radioactive decay of rubidium-87 to strontium-87 is 4.88 × 10 years. Suppose nuclear chemical analysis shows that there is 0.728 mmol of strontium-87 for every 1.000 mmol of rubidium-87 in a certain sample of rock. Calculate the age of the rock. Round your answer to 2 significant digits. ☐ years x10 n ?