The two lines on the bottom triangle of the parallelogram indicate that it is an isosceles triangle. Therefore, angles BAD and ADB are equal.
And we know that all the angles in a triangle equal 180 degrees. So those two angles must equal 152 (180-28)...so half of that is 76 degrees.
Because this is a parallelogram, angle BAD=angle DCB, which is 76 degrees
So, angle DCB=76 degrees.
