Answer:
System of linear equations

a: adult ticket price and c: child ticket price
Step-by-step explanation:
This system of equations can be used to find the price of the adult and child tickets.
We have two equations (one for each day) and two unknowns (adult ticket price and child ticket price).
Let a: adult ticket price and c: child ticket price,
we have for the first day that 3 adult tickets and 1 child ticket adds $38:

and for the second day we have that 2 adult tickets and 2 child tickets adds $52:

If we write this as a system of equations, we have:

<h3>
Answer: B) Linear pair postulate</h3>
Explanation:
As the name implies, "linear pair" means the two angles combine to form a straight line of 180 degrees. Think of gluing the angles together.
As an example, let's say angle 1 was 50 degrees and angle 4 is 130 degrees. They combine to 50+130 = 180 which is a straight angle. I recommend using a protractor to help draw these angles.