At a Particular Time, a Radioactive Source a Has a Strength

Multiple Choice

At a particular time, a radioactive source A has a strength of 1.60 *10¹¹ Bq and a half-life of 8.00 days, and a radioactive source B has a strength of 6.40 *10¹¹ Bq. The two sources have the same strength 30.0 days later. The half-life of source B is

A) 35.7 days.
B) 24.7 days.
C) 17.2 days.
D) 7.53 days.
E) 5.22 days.