The property used in #20 was called 'the distributive property'.
This property gets rid of the parenthesis and also gets the expression more simple. 
x(y+b)
x*y + x*b              ⇔ Notice the change here? 
Answer would be: Distributive property 
        
             
        
        
        
Let
x = 3a (first angle)
y = 3a (second angle)
z = 6a (third angle)
The total angle of a triangle is ALWAYS 180.
3a + 3a + 6a = 180
12a = 180
a = 15
Therefore, x = 45, y = 45, z = 90
        
             
        
        
        
Answer:
23
Step-by-step explanation:
 
        
             
        
        
        
Answer:
X= 2
Step-by-step explanation:
10 + x = -12
X = 12 - 10
X = 2