Question 2 (6 marks) To investigate the efficacy rate of COVID19 vaccine on children aged 3 to 11, a doctor conducted a survey with a random sample of size 600. The survey result showed that 75% of the selected children have received at least one dose of COVID19 vaccine, 15% of them are infected by COVID19, 14.5% of them are unvaccinated and not infected by COVID19. (a) What is the probability of selecting a child who is vaccinated and not infected by COVID19? (3 marks) (b) Among the vaccinated children, how many of them are infected by COVID19? (3 marks)