A specic radioactive substance follows a continuous exponential decay model. It has a halflife of 18 minutes. At the start of the experiment, 665.3 g is present. (a) Let t be the time (in minutes) since the start of the experiment, and lety 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. (b) How much will be present in 8 minutes? Do not round any intermediate computations, and round your answer to the nearest tenth. Dg