please answer to the question in the attachment.....

1)

A sample of a radioactive substance decayed to 90.5% of its original amount after a year. {Round your answers to two decimal places.) (a) what Is the half-life of the substance? yr (b) How long would It take the sample to decay to 40% of Its original amount? yr Scientist can determine the age of ancient objects by a method called radiocarbon dating. The bombardment of the upper atmosphere by cosmic rays converts nitrogen to a radioactive Isotope of carbon, 1\"C, with a half-life of about 5?30 years. Vegetation absorbs carbon dioxide through the atmosphere and animal llfe assimilates I4C through food chains. When a plant or animal dles, it stops replacing its carbon and the amount of 14C begins to decrease through radioactive decay. Therefore, the level of radioactivity must also decay exponentially. A parchment Fragment was disoovered that had about 75% as much 14(2 radioactivity as does plant material on Earth today. Estimate the age of the parchment. (Round your answer to the nearest hundred years.) yr