Answer:
x = 13
Explanation:
The sum of angles in a quadrilateral is 360°, so you have ...
75° + 6x° + 90° +9x° = 360°
15x +165 = 360 . . . . . collect terms, divide by °
x + 11 = 24 . . . . . . . . . divide by the coefficient of x
x = 13 . . . . . . . . . . . . . subtract 11
_____
Check
6x° = 78°
9x° = 117°
75° + 78° +90° +117° = 360° . . . . as required.