Answer: 6
Step-by-step explanation:
Ok lemme actually format this set
[tex]$C = \left\{\frac 1x : x \in \mathbb{Z}\ \text{and}\ 4 \leq x \leq 9\right\}$[/tex]
Well the only integers from 4 to 9 are 4, 5, 6, 7, 8, 9. So this set is just
[tex]$C = \left\{\frac 14, \frac 15, \frac 16, \frac 17, \frac 18, \frac 19\right\}$[/tex]
which has cardinality [tex]\boxed{6}[/tex] .
