trontium-90 is a radioactive material that decays according to the function A(t) = A e -0:02441, where Ao is the initial amount present and A is the amount preser me t (in years). Assume that a scientist has a sample of 800 grams of strontium-90 a) What is the decay rate of strontium-90? b) How much strontium-90 is left after 30 years? c) When will only 200 grams of strontium-90 be left? (d) What is the half-life of strontium-90? (a) The decay rate of strontium-90 is % (Type an integer or a decimal. Include the negative sign for the decay rate.) (b) Approximately grams of strontium-90 is left after 30 years. (Do not round until the final answer. Then round to the nearest whole number as needed.) (c) Only 200 grams of strontium-90 will be left in about years (Do not round until the final answer. Then round to the nearest tenth as needed.) (d) The half-life of strontium-90 is approximately years (Do not round until the final answer. Then round to the nearest tenth as needed.)