(i) From figure , it is clear that angle between the lines joining stalls C,D and stalls C, B is ∠BCD . Given, ∠DBC = 60° and ∠BAC = 40° CD is a chord of circle. Here, ∠CBD and ∠CAD are angles in the same segment of the circle. ∴ ∠CAD = ∠CBD = 60° Now, ∠BAD = ∠BAC + ∠CAD = 40° + 60° =100° Since, ABCD is a cyclic quadrilateral. ∠BAD + ∠BCD =180° ⇒ 100° + ∠BCD =180° ⇒ ∠BCD =180°-100° ⇒ ∠BCD = 80° Hence, angle between the lines joining stalls C, D and stalls C, B is 80°. (ii) Yes, such activities are helpful for society. (iii) Other social issues for which such compaigns are required, are old age home, orphanages, etc.