Please help with the attached question:

There are two risk factors than have been discovered for a particular disease. 80% of the population has no risk factors. 15% have risk factor A only, 4% have risk factor B only and 1% have both risk factors. If an individual has no risk factors, their probability of developing the disease is 0%. If they have a single risk factor, their probability of developing the disease is 20%. If they have both risk factors, their probability of developing the disease is 90%