In an observational study investigating the association of cognitive impairment and cortical thinning in older adults, researchers gathered 49 subjects with mild cognitive impairment (MCI), and 40 healthy controls (no CI). All individuals underwent MRI scans to measure cortical thinning in various areas of the temporal lobe. Individuals' measures of cortical thinning were aggregated and classified as normal age-related thinning, or increased thinning. Use the following table to answer the questions below.

normal thinning increased thinning total
MCI 21 28 49
no CI 22 18 40
total 43 46 89

Required:
a. What is the probability that a study subject has MCI and normal age-related cortical thinning?
b. What is the probability that a study subject has MCI given that they exhibit increased cortical thinning?