I believe Jacqueline may be confusing the length of the side of the triangle and it's height, which are two different things. (It's a common mistake).
Imagine the that leaning triangle is a building and someone asks you for the height of that building. What are they really asking you? Are they asking you how long the side of the building is? No. They are asking you the distance from the tip of that building to the ground.
Better yet. Pretend they ask you to drop something from the top of that building. What path will it follow? Will it follow a path down the side of the triangle? No. It will follow a path straight down. That is your height. That path straight down is the height of the triangle. That path is the dotted line from Y to W.
If you want to know the height of any triangle draw a line extending in both directions from the base. Draw a parallel line to the base that just touches the opposing vertex of the triangle. That distance between those two parallel lines, which is the length of a perpendicular line between them, is the height of your triangle.
It might seem like they are making a mistake in asking for the area of XYZ, but it is not. The question is designed to make sure one knows that the height of a triangle is not the same as the length of it's side.
Another thing, as for how we know the base of XZ is 6. It was given.
Here is another problem that implicitly covers the same subject: (
https://greprepclub.com/forum/in-the-fi ... tml#p38039).
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