I am having trouble with Question 14 part A and B

14 The SIRstyle diagram in Figure 21.8 demonstrates the dynamics of a new disease called ctitia that is sweeping the nation. Fictitia is different from the disease we diagrammed in Section 21.2 in a number of ways: 0 There is no vaccine for ctitia and no way to recover from it, so there is no recovered population. . Fictitia renders patients sterile, so the birth rate is proportional to the size of the susceptible population, not the whole population. 0 Fortunately, there are some costly selfprotective activities h that people can take to avoid contracting ctitia. Their rate of use depends on both the cost of the activities ,0 and the prevalence of the disease 1\