Answer:
Scale factor  = 3
Step-by-step explanation:
Using similar triangles
AT/AG = AB/AC
9/3 = x+10/3x-10
Cross multiply
3(x+10) = 9(3x-10)
Expand
3x+30 = 27x-90
3x-27x = -90 - 30
-24x = -120
x = 120/24
x = 5
For the larger triangle;
AC = 3x-10
AC = 3(5)-10
AC =15-10
AC = 5
AB = x+10
AB = 5+10
AB = 15
For the scale factor;
Since AT/AG = AB/AC
9/15 = 3/5
3*3/5*3 =3/5
Since the numerator and denominator of the larger triangle is multiplies by the same factor i.3 3. Hence the scale factor is 3 
 
        
             
        
        
        
Answer:
16 years
Step-by-step explanation:
Given data
For the first tree
let the expression for the height be
y=4+x--------------1
where y= the total height
           4= the initial height
           x= the number of years
For the second tree, the expression is
y=12+0.5x-------------2
Equate 1 and 2
4+x=12+0.5x
x-0.5x=12-4
0.5x= 8
x= 8/0.5
x=16
Hence it will take 16 years for both trees to have the same height
 
        
             
        
        
        
Since two people take both courses, we can subtract two from 7, 8, and 21, giving us 5, 6, and 19. 
Add 5 and 6 together to get 11. Since eleven students are in those two groups, we can answer this. The answer will be 11/19.
        
             
        
        
        
Additive Identity Property is the answer.