An equation of the radioactive decay in this case is= , where C is the initial mass of carbon-14 in the sample; t is the time in years. Simplify and solve for "t", which is the major unknown in this case. Start canceling "C" in both sides. = 0.76 Take logarithm base 2 from both sides -t/5600 = -t/5600 = -0.39593 t = 5600*0.39593 = 2217 years. ANSWER