What is the value of x in this figure?

I believe the answer is B

There are two known angles in this triangle, 30 and 90. This means that the third missing angle is 60, which makes this triangle a 30-60-90 triangle.

30-60-90 triangles have special side lengths, as indicated in the picture attached to this answer.

We know that the hypotenuse side length is 10. In the diagram attached to this answer, the hypotenuse side length is equal to 2x, which means that 10 = 2x. Solve for x by dividing both sides by 2:



x is equal to 5.

Because the figure asks for the missing side length of the adjacent side, we can plug in the value of x into the diagram attached to this picture, which means that the value of x in the figure is 5√3.