x = 5
Since it’s a parallelogram, the sides are parallel to each other and the diagonal acts as a transversal
Alternate interior angles are congruent so you can set them equal to each other
5x - 3 = 14x - 48
Subtract 5x from both sides
-3 = 9x - 48
Add 48 to both sides
45 = 9x
Divide both sides by 9
5 = x
~~hope this helps~~