The answer choices are 10, 15, 30, 35.​

Lets us start with finding the inner angles of the triangle. The bottom right angle shall be 70 degrees as it is opposite. The 100 degrees shall add together to make 200. 360-200 = 160. 160 / 2 = 80. So, Now we know bottom left angle (80) and bottom right (70). 80 + 70 = 150. In a triangle, angles add to 180 so 180 - 150 = 30. 30 = 2x which means that x = 15

15