A specific radioactive substance follows a continuous exponential decay model. It has a half-life of 7 hours. At the start of the experiment, 58.8 g is present. (a) Let t be the time (in hours ) since the start of the experiment, and let y be the amount of the substance at time t. Write a formula relating y to t. Use exact expressions to fill in the missing parts of the formula. Do not use approximations. y=â–¡ e^(â–¡) t (b) How much will be present in 19 hours ? Do not round any intermediate computations, and round your answer to the nearest tenth. g