Use the law of cosines to solve for angle A. Plug your known side length values into the equation a^2 = b^2 + c^2 – 2bc cos A.
Then use the law of sines to find angle B. (Sin A/a = Sin B/b = Sin C/c).
Because the two red angles within B are congruent, divide your angle measure in half.
From there, do the law of sines to solve for x. Good luck!
I hopes this helps