Radioactive strontium, ⁹⁰Sr, has been deposited in a large field by acid rain. If sufficient amounts make their way through the food chain to humans, bone cancer can result. It has been determined that the radioactivity level in the field is 2.8 times the safe level S. ⁹⁰Sr decays according to the formula

A(t) = A₀e^0.0239t,

where A₀ is the amount currently in the field and t is the time in years. For how many years will the field be contaminated? (Round your answer to one decimal place.)