Question 433634
First of all, the sum of all the angles of a quadrilateral is 360 degrees.  Consider the special case of a square or rectangle.  
In this case, we know all 4 angles are right angles, so the sum of all the angles = 90+90+90+90=360.
Secondly, if the angles given in the problem are 138,x,x,3x+20, then the figure cannot be a parallelogram.  
In a parallelogram opposite sides are parallel, and opposite angles are equal.  
If we solve for x, we get:
138 + x + x + 3x + 20 = 360
5x = 360 - 158
x = 40.4
This would give the following angles:
138,40.4,40.4,141.2
These angles cannot form a quadrilateral.  If two of the angles are equal, then the other two must also be equal.