Which of the following is an empty set?

Let the relation $$R$$ be defined in $$N$$ by $$a R b$$, if $$3 a+2 b=27$$, then $$R$$ is

Suppose that the number of elements in set $$A$$ is $$p$$, the number of elements in set $$B$$ is $$q$$ and the number of elements in $$A \times B$$ is 7, then $$p^2+q^2=$$

Let the relation $$R$$ is defined in $$N$$ by $$a R b$$, if $$3 a+2 b=27$$ then $$R$$ is