First, recall that the equation of a line is
y = mx+b
where 
m = slope
b = y-int
The key to this question is the details :
Horizontal line ---> This tells you that your slope is 0
y-int = 3.5 -----> In the equation above, b=3.5
Therefore,
y = 0x + 3.5
y = 0 + 3.5
y = 3.5
        
             
        
        
        
Answer:

Step-by-step explanation:
Let  denotes number of pencils, markers, erasers respectively.
 denotes number of pencils, markers, erasers respectively.
For Andrea:

For Justin:

For Virginia:

On subtracting equations (i) and (ii), we get

Put  in equation (i)
 in equation (i)

Put  in equation (iii)
 in equation (iii)

Multiply equation (iv) by 5 and equation (v) by 6 and then subtract both the equations.

Put  in equation
 in equation 

Put  in equation (i)
 in equation (i)

 
        
             
        
        
        
First one= x=5
second one= x=1/30 or 0.03 or 30^-1
third one= All real numbers or R
fourth one= No solution
Fifth one= All real numbers or R
Sixth one= p=-10/3 or -3 1/3 or -3.3
R is just the symbol for all real numbers. Also know as infinitely many solutions. 
Hope this helps ! :) have a good day! Make sure you eat.
        
             
        
        
        
Answer:
C. The trails are not independent.