A sample of 400g of radioactive lead-210 decays to polonium-210 according to the function A(t)= 400e 0.032 t where t is time in years. Find the amount of radioactive lead remaining after (a) 4 yr, (b) 8yr, (c) 15yr. (d) Find the half-life.

(a) amount of radioactive lead remaining after 4 yr will be nothing

(Round to the nearest integer as needed.)

(b) The amount of radioactive lead remaining after 8yr will be nothing g.

(Round to the nearest integer as needed.)

(c) The amount of radioactive lead remaining after 15yr will be nothing g.

(Round to the nearest integer as needed.)

(d) The half-life is about nothing yr.

(Round to two decimal places as needed.)