The answer is choice C cos(x)=10/15.
 
        
                    
             
        
        
        
Consider, pls, this option:
1. if a required line has a form y=ax+b, then points A(-1;6); B(6;k) and C(20;3) belong to it.
2. According to the item 1 it is possible to make up the system of equations for A and C:

Knowing, that a=-1/7 and b=41/7, it is possible to write the equation of required line:

3. Using coordinates of point B:

Answer: 5.
 
        
        
        
Number of students N, y years
N = 700 + 50y   
N = 700 + 50 x 10 = 1200   (C)
Left not painted percentage = 100 - 60 = 40 %
Left = 40/100 x 45 =  18 (H)
        
             
        
        
        
Answer:
21
Step-by-step explanation:
Let x = the number 
12x-12 = 240
12x = 252
x = 21