Alright, so what we can take as a given is that arcDE/2= ∠CDE=2x+20 since the arc corresponding to the angle is 2*the angle. To solve for arcDE, we multiply both sides by 2 to get 2(2x+20)=4x+40=arcDE. Since the arcs in a circle add up to 360 degrees and we only have -20+30x and arcDE, we have -20+40+4x+30x=360 using the associative property. Simplifying, we get 20+34x=340. Subtracting 20 from both sides, we get 340=34x. Next, we can divide both sides by 34 to get 10=x.
So all the angles in total are going to be 180 degrees.
7+9+10 = 18 (parts at all)
180/18=10 (1 part of the ratio)
Than to find all of the angles we multiply 1 part by 7, 9 and 10 separately
10*7= 70 degrees (1st angle)
10*9=90 degrees (2nd angle)
10*10=100 degrees (3rd angle)
Answer: 70, 90, 100