The solution set of $x \equiv 3 \pmod{7}$,where $x \in \mathbb{Z}$,is:

Let $R$ be a relation from $N$ to $N$ defined by $R = \{(a, b) : a, b \in N \text{ and } a = b^2\}$. Is the following statement true?
$(a, b) \in R$ implies $(b, a) \in R$

If $R = \{(a, b) : b = a - 1, a \in \mathbb{Z}, 5 < a < 9\}$,then the range of $R$ is

Let $R$ be a relation on $N$ defined by $x + 2y = 8$. The domain of $R$ is

Let $A = \{2, 3, 4, 5\}$ and $B = \{3, 6, 7, 10\}$. $A$ relation $R$ is defined from $A$ to $B$ such that $xRy \iff x$ is relatively prime to $y$. What is the domain of $R$?

If $A = \{(a, b) : 4a = 5b; a, b \in \{1, 2, 3, \dots, 30\}\}$,then the number of such ordered pairs $(a, b)$ is