What Would the Atom Ratio of ²⁰⁶Pb to ²³⁸U Be

Multiple Choice

What would the atom ratio of ²⁰⁶Pb to ²³⁸U be in a uranium mineral from a rock that is 1.0 * 10⁹ years old? t_1/2(²³⁸U) = 4.5 * 10⁹ yr.

A) 0.14
B) 0.16
C) 0.22
D) 0.86
E) 1.16