(a)
Given data:
The given set is {-1, 6, 3,1, a}.
The set {a, 1, 7} is not subset of the given set.
[tex]\mleft\lbrace a,\text{ 1, 7}\mright\rbrace⊄\mleft\{-1,6,3,1,a\mright\}[/tex]
Thus, the symbol must be used is ⊄.
(b)
Given data:
The given set is {3, 5,7,9}.
The number 3 is belongs to the given set.
[tex]3\in\mleft\lbrace3,\text{ 5, 7, 9}\mright\rbrace[/tex]
Thus, the symbol used in the above expression is ∈.
