Is that a parallelogram with its lower left corner "cut off"? If so, then imagine that you have this corner. It would form a triangle, with two of angles being are supplemental angles of 3x and 132°. The 3rd would have be 2x.
The sum of these angles is 180°, so the equation is
$\displaystyle (180^{\circ} - 3x) + 48° + 2x = 180^{\circ}$.
Solve for x.
Look at the attached diagram:
I've added a "corner" to the parallelogram in your original drawing, and then I enlarged the corner. I'm assuming that this "corner" forms a triangle. The sum of angles a, b, and 2x has to equal 180°.
Angle a is the supplement of 3x, so $\displaystyle a = 180^{\circ} - 3x$. Angle b is the supplement of 132°, so $\displaystyle b = 180^{\circ} - 132^{\circ} = 48^{\circ}$. Therefore, the sum of the angles in this triangle is
$\displaystyle (180^{\circ} - 3x) + 48° + 2x = 180^{\circ}$.