What Is the Time Needed for the Activity of a Radium-226

What is the time needed for the activity of a radium-226 source to change from 1.5 Ci to 0.50 Ci? (The half-life of radium-226 is 1.60 * 10³ y.)

A) 5.33 * 10² y
B) 1.60 * 10³ y
C) 1.10 * 10³ y
D) 9.36 * 10² y
E) 2.54 * 10³ y