Please clearly refer the formula or concept which will be used to solve this problem.

heartworm is a serious disease, D, that has been found in 0.01 percent of dogs. A researcher has formulated a test that will be positive, p. for 98 percent of dogs who have heartworm and be positive for 3 percent of dogs who do not suffer from heartworm. Find the probability that a randomly selected dog tested as positive does not have heartworm