The cardinality of the set (A − C) n B is 35 .
We have given three sets A = {x | x ≤ N} where N is a natural number .
Then , set A will get values [tex]A= \{1,2,3,4,5......\}[/tex]
B = {x-5 < x < 105, x ≤ R} where R is a real number whose values is in domain of (- ∞ ,∞)
Then , set B will get values [tex]B=(-5,105)[/tex]
C = {x|x is a rational number, 10 < x < 80} rational number which can expressed in [tex]\frac{p}{q}[/tex] where [tex]q\neq 0[/tex] .
Then , set C will get values [tex]=(10,80][/tex]
According to the question
(A − C) n B [tex]=(\{1,2,3,4,5 ........\}-(10,80] \sqcap (-5,105)[/tex]
[tex]=\{1,2,3,4,5,6,7,8,9,10,81,82,83 .......\} \sqcap (-5,105)\\[/tex]
={1,2,3,4,5,6,7,8,9,10,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103, 104 ,105}
Learn more about set here :
https://brainly.com/question/2166579
#SPJ9