After the release of radioactive material into the atmosphere from a nuclear power plant in a country in 1991

1991, the hay in that country was contaminated by a radioactive isotope(half-life 5

5 days). If it is safe to feed the hay to cows when 12

12% of the radioactive isotoperemains, how long did the farmers need to wait to use thishay?

The farmers needed to wait approximately

nothing _______ days for it to be safe to feed the hay to the cows.