Given, A={1,2,3,4,5},B={4,5,6,7,8},C={7,8,9,10,11} and D={10,11,12,13,14}.
For B∪C∪D
B∪C ={4,5,6,7,8} ∪ {7,8,9,10,11}
B∪C ={4,5,6,7,8,9,10,11}
Now, B∪C∪D = (B∪C)∪D
B∪C∪D ={4,5,6,7,8,9,10,11} ∪ {10,11,12,13,14}
B∪C∪D ={4,5,6,7,8,9,10,11,12,13,14}
Hence,
B∪C∪D ={4,5,6,7,8,9,10,11,12,13,14}