The set C and D are defined by C ( x : x < 8 ) and D = x :3x <_ 15 where x is a counting number list the elements of C and D ( b) find C intersect D

Counting numbers are positive integers: 1, 2, 3, 4, ...

C = {x : x < 8, where x is a counting number}
The counting numbers less than 8 are 1, 2, 3, 4, 5, 6, 7.
C = {1, 2, 3, 4, 5, 6, 7}

D = {x : 3x ≤ 15, where x is a counting number}
First, solve the inequality:
3x ≤ 15
x ≤ 15/3
x ≤ 5
The counting numbers less than or equal to 5 are 1, 2, 3, 4, 5.
D = {1, 2, 3, 4, 5}

C = {1, 2, 3, 4, 5, 6, 7}
D = {1, 2, 3, 4, 5}
The elements that appear in both sets are 1, 2, 3, 4, 5.
C intersect D = {1, 2, 3, 4, 5}