This triangle is a 30-60-90 triangle, which you can just find by solving for the unknown angle in the triangle, making it a 30-60-90 triangle.
You'll need to memorize the side lengths for these triangles, but the side opposite from the hypotenuse (x in this case), will be half the length of the hypotenuse.
Meaning that
![2x=8](https://img.qammunity.org/2021/formulas/mathematics/middle-school/kz2753b52nzwd5gu7qpr8kpwnqu0vr88lx.png)
So
![x=4](https://img.qammunity.org/2021/formulas/mathematics/middle-school/a1fs70p5exgs68ljexkqkiueya3liaz52t.png)
Hope this helps.
頑張って!