Can you help me understand how to solve this problem?

For the use of a test for a certain disease, the sensitivity is 0.83, the specificity is 0.9, and the prevalence is 0.002. a. Given that a test is positive, find the probability that a random patient has the disease. b. Draw a tree diagram for a typical sample of 1000 patients. c. Of the cases that are positive, explain why the proportion in error is larger if the prevalence is lower