Answers:

(i)

B = {4, 5, 6, 7, 8}

C = {7, 8, 9, 10, 11}

B ∪ C = {x: x ∈ B or x ∈ C}

∴ B ∪ C = {4, 5, 6, 7, 8, 9, 10, 11}

(ii)

B = {4, 5, 6, 7, 8}

D = {10, 11, 12, 13, 14}

B ∪ D = {x: x ∈ B or x ∈ D}

∴ B ∪ D = {4, 5, 6, 7, 8, 10, 11, 12, 13, 14}