Get a ruler that measures mm's and cm's. Count how many mm's in one cm. 1 cm=10 mm.
How many ______cm=_80 mm? You can set up a proportion to solve this problem if you want.
Then you could cross multiply: 10X=80 Then divide both sides by 10.
Finally, just use your centimeter ruler to draw the horizontal line segment. Make it parallel and horizontal to the bottom of the paper. You can draw an endpoint. Then draw a vertical, perpendicular(straight down, 90º) segment from the endpoint to the bottom of the paper. Then draw another vertical, perpendicular segment from the other endpoint to the same specific distance down. Opposite sides are now equal, and you have a horizontal side to the side of the bottom of the paper. You know now that the line segment originally drawn is horizontal.
If you have further questions, then just ask me. If I have helped you, please give me a thumbs up.
._______________. Example of a horizontal segment
How do you define a segment? If you took a line and cut a piece out of it, you would have a segment. Also, there is an end point at the end of each segment. Segments don't go on forever like a line does.