Question 1084576
 {{{A}}}={{{3}}},{{{5}}},{{{7 }}}

the cardinality of a set is the number of elements it contains; so, 
the cardinality of a set {{{A}}} is {{{3}}}

all possible subsets are:

∅ or {{{aleph-zero }}}

{{{ 3}}}

{{{ 5}}}

{{{ 7}}}

{{{3}}},{{{5 }}}

{{{ 3}}},{{{7}}}

{{{5}}},{{{7 }}}

{{{ 3}}},{{{5}}},{{{7}}}