Given that quadrilateral QRST is a square.
Each angle of a square is of 90 degrees.
Angle <RQT is also an angle of 90 degrees.
We also given angle RQT = 3x - 6.
So, we can setup an equation as 3x-6 =90.
Now, we need to solve the equation for x.
6 is being subtracted from left side.
We always apply reverse operation. Reverse operation of subtraction is addition.
So, adding 6 on both sides of the equation, we get
3x-6+6 =90+6.
3x = 96.
3 is being multipied with x, in order to remove that 3, we need to apply reverse operation of multiplication.
So, dividing both sides by 3.
x=32 (final answer).