Because there are 4 inside angles the sum of the four angles must equal 360 degrees.
Add the angles to equal 360:
4x + 3x + 2x + 3x = 360
Simplify:
12x = 360
Solve for x by dividing both sides by 12:
x = 360 /12
x = 30
Now you have x, solve for each angle:
ABC = 4x = 4 x 30 = 120 degrees.
BCD = 3x = 3 x 30 = 90 degrees.
CDA = 2x = 2x 30 = 60 degrees.
DAB = 3x = 3 x 30 = 90 degrees.
C. It's important to know that a four sides figure needs the inside angles when added together need to equal 360 degrees.