Strontium 90 is a radioactive material that decays according to the function A(t) = A₀e^-0.0244t where A₀ is the initial amount present and A is the amount present at time t (in years). Assume that a scientist has a sample of 500 grams of strontium 90.

(a) What is the decay rate of strontium 90?

(b) How much strontium 90 is left after 10 years?

(c) When will 400 grams of strontium 90 be left?

(d) What is the half-life of strontium 90?