The set $A = \{ x : x \in \mathbb{R}, x^2 = 16 \text{ and } 2x = 6 \}$ is equal to

State whether the following set is finite or infinite:
The set of animals living on the earth.

In each of the following,determine whether the statement is true or false. If it is true,prove it. If it is false,give a counterexample.
If $A \subset B$ and $B \in C,$ then $A \in C$.

If ${N_a} = \{an : n \in N\}$,then ${N_3} \cap {N_4} = $

Write the following interval in set-builder form: $(6, 12]$

Write the following set in the set-builder form: $\{ 1, 4, 9, \ldots, 100 \}$