Answer:
x = 11
Explanation:
You want to know the measure of x in a square marked with one portion of the bisected corner angle as being (6x -21)°.
Angle
We presume quadrilateral PQRS is a square, so each of the corner angles is 90°, and each of the diagonals bisects the corner angles. That mean ...
(6x -21)° = 90°/2
6x = 66 . . . . . . . . . . divide by °, add 21
x = 11 . . . . . . . . . . . divide by 6