SOLUTION: If B={x e W and x < 5 }and C={x:x e N, 5 < x < 10}, find the elements of the set B and C also find n(A) and n(B)

W is the set of WHOLE numbers which are 0,1,2,3,4,5,6,... etc.

B={x e W and x < 5}

So B is the set of whole numbers that are less than 5:

so B = {0,1,2,3,4}

N is the set of NATURAL numbers which are {1,2,3,4,5,6,7,... etc.

C={x:x e N, 5 < x < 10}

So C is the set of natural numbers greater than 5 and also less than
10. Or you might say, the ones between 5 and 10, not including 
5 or 10, 

so C = {6,7,8,9}

[You didn't mention any set A. Was that an error?  I will answer 
n(B) and n(C) instead.]

n(B) and n(C) asks us to count how many there are in the sets 
B and C.

Since B = {0,1,2,3,4}, n(B) = 5 because it contains 5 elements.

Since C = {6,7,8,9}, n(C) = 4 because it contains 4 elements.

Edwin