This problem uses isoceles triangles and sum of angles and vertical angles
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Lets see:
BAC is 28 degrees, and since ABCD is a rectangle, DAB is 90 degrees.
So that means DAC is 90 - 28 = 62 degrees.
That also means that DCA is 28 degrees because of vertical angle theorem (keep that in mind)
The sum of the angles of triangle DAQ is 180 degrees.
So since DQA is 90 degrees as given, and DAC is 62 degrees.
Angle ADQ is 180 - 90 - 62 = 28 degrees.
Angle ADC is a right angle, so 90 - 28 = 62 degrees. QDC is 62 degrees.
And since DCA is 28 degrees,
Angle QDP is 62 - 28 = 34 degrees