Question

A ={X | X ∈ N ,3 | X , X ≤ 21}
B ={x | x ∈ N , 5 | x , x ≤ 25}
C ={x | x ∈ N , 2 | x , x ≤ 20}

Answer 1

A ={X | X ∈ N ,3 | X , X ≤ 21}={0. 3. 6. 9. 12. 15. 18. 21]

B ={x | x ∈ N , 5 | x , x ≤ 25}={0. 5. 10. 15. 20. 25}
C ={x | x ∈ N , 2 | x , x ≤ 20}={0, 2, 4, 6,8,10,12,14,16,18,20}