Hello!
When you translate something horizontally, its x value changes. This is because you are shifting it from left to right or right to left, and the x value is what measures this.
In this case, if you are shifting the triangle 6 units horizontally (I'm assuming to the right), you are therefore changing the x value by 6. In this case, you are moving the triangle in the positive direction, meaning the x value will increase by 6.
Hope this helps!