Answer:
H = 58, I = 71, J = 51
Explanation:
Set all angles equal to 180
3x - 2 + 4x - 9 + 3x - 9 = 180 
Then combine like terms 
10x - 20 = 180 
 + 20 + 20 
10x = 200 
/10 /10 
x = 20 
Then plug in for each angle 
3 (20) - 2 = 58 
4 (20) - 9 = 71 
3 (20) - 9 = 51