Answer:
c < 7
Explanation:
The cardinal indicates the number or quantity of the elements of a set, be this finite or infinite quantity.
Given, A = {1, 2, 42, 57, 99, 538, 677}
B = {1, 5, 6, 7, {2, 3} }
C = {1, {7}, {8, 9} }
Let's say the cardinality of the subset is: c
Inequality that represents the cardinality of any proper subset of A is: c < 7
Hope this helps!