Although bismuth is generally considered stable, its only natural isotope, bismuth-209, is estimated to have a half-life

Question:

Although bismuth is generally considered stable, its only natural isotope, bismuth-209, is estimated to have a half-life of 1.9 × 1019 y. If the universe is estimated to have a lifetime of 1.38 × 1010 y, what percentage of bismuth-209 has decayed over the lifetime of the universe?