Answer: x = 30
Step-by-step explanation:
Since AB and CD are straight lines, vertical angles formed by them are congruent. Angle DOB is equal to angle AOC which is equal to 2x. Since you know that a straight angle is equal to 180 degrees, you can say :
2x + 90 + x = 180
3x + 90 = 180
3x = 90
x=30
Hope this helped :)