### Theory:

The number line is that we commonly use the horizontal line of the coordinate axis. In a Number line, usually zero is in the middle, and the positive numbers are to the right side of the zero and the negative numbers to the left.
• A straight coordinate line is also called Number line.
• A numerical representation of a point's location is called a point coordinate.
If a coordinate origin is marked, on a line, then the line turns into a number line (therefore, the point corresponding to $$0$$). The positive axis represents to the right or up and is mark by an arrow in the drawing.

The figure shows that the coordinates start at C.
The coordinate of point A is $$-3$$.
The coordinate of point B is $$-1$$.
The coordinate of the point D is approximately $$2.5$$.
The coordinate of point E is $$4$$.

Brief record is as follows: A ($$-3$$); B ($$-1$$); C ($$O$$); D ($$2.5$$); E ($$4$$).

Of the given points, positive values ​​are for points $$D$$ and $$E$$, while negative values ​​are for $$A$$ and $$B$$.