Carbon-14 decays exponentially with a half-live of 5700 years. (a) Find the value of r in A(t) = apert for t in years. Give the exact value and a decimal approximation. (b) An Egyptian mummy is discovered in which the amount of carbon-14 present is only about two- thirds the amount found in the atmosphere. How long ago was the mummy buried? (c) Another Egyptian mummy is estimated to contain 59% of the carbon-14 in contained originally. How long ago was the mummy buried?