3. Polonium-210 has a half-life of 140 days. It decays exponentially, where rate of decay is proportional to the amount at the time t. If we start with 100 g , how much will remain after 10 weeks?
(A) 50
(B) 71
(C) 90
(D) 280
(A) 50
(B) 71
(C) 90
(D) 280