Since the two given angles, angle C and angle A, are across from each other inside the quadrilateral, that means that they add to 180 degrees
A + C = 180
2x + 9 + 3x + 1 = 180
combine like terms
5x + 10 = 180
subtract 10
5x = 170
divide both sides by 5
x = 35
Angle A is (2x + 9)
2(35) + 9
70+9
Angle A is 79 degrees.
Hope this helps!
