There is actually a cool trick to this. When you see a and 2a, in this case 6 and 12, then the small triangle is a 60-30-90 triangle. The remaining side is
.
This value rounds down to 10, and yep, you guessed it, another 30-60-90.
This time, x =
.
This is a very difficult problem and requires knowledge of the special triangles. Hope this helps!