In a cohort breast cancer study, a woman is considered to be "exposed" if she first gave birth at age 30 or older. In a sample of 4540 women who gave birth to their first child before the age of 30, 65 developed breast cancer. Of the 1628 women who first gave birth at age 30 or older, 31 were diagnosed with breast cancer. Estimate the percentage of the disease among the exposed that is attributed to the exposure.
Select one:
a. 8%
b. 18%
c. 25%
d. 34%