A sample of a radioactive substance has an initial mass of 795.3 mg. This substance follows a continuous exponential decay model and has a half-life of 6 minutes. (a) Let t be the time (in minutes) 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 = 795.3e' (b) How much will be present in 19 minutes? Do not round any intermediate computations, and round your answer to the nearest tenth. O mg