If $A$ and $B$ are two sets such that $A \subset B$,then what is $A \cup B$?

If $A = \{x \mid x \in N, x \text{ is a prime number less than } 12\}$ and $B = \{x \mid x \in N, x \text{ is a factor of } 10\},$ then $A \cap B = \dots$

If $A = \{x : x \text{ is a multiple of } 4\}$ and $B = \{x : x \text{ is a multiple of } 6\}$,then $A \cap B$ consists of all multiples of:

The simplified switching circuit for the following circuit is

$A$ class has $175$ students. The following data shows the number of students opting for one or more subjects: Mathematics $100$,Physics $70$,Chemistry $40$; Mathematics and Physics $30$,Mathematics and Chemistry $28$,Physics and Chemistry $23$; Mathematics,Physics,and Chemistry $18$. How many students have opted for Mathematics alone?

Find the union of each of the following pairs of sets:
$A = \{1, 2, 3\}, B = \varnothing$